HTML5

manifest

DOM interface:

interface HTMLHtmlElement : HTMLElement {};

The html element represents the root of an HTML document.

The manifest attribute gives the address of the document's application cache manifest, if there is one. If the attribute is present, the attribute's value must be a valid non-empty URL potentially surrounded by spaces.

The manifest attribute only has an effect during the early stages of document load. Changing the attribute dynamically thus has no effect (and thus, no DOM API is provided for this attribute).

For the purposes of application cache selection, later base elements cannot affect the resolving of relative URLs in manifest attributes, as the attributes are processed before those elements are seen.

The window.applicationCache IDL attribute provides scripted access to the offline application cache mechanism.

The html element in the following example declares that the document's language is English.

<!DOCTYPE html>
<html lang="en">
<head>
<title>Swapping Songs</title>
</head>
<body>
<h1>Swapping Songs</h1>
<p>Tonight I swapped some of the songs I wrote with some friends, who
gave me some of the songs they wrote. I love sharing my music.</p>
</body>
</html>

4.2 Document metadata

4.2.1 The `head` element

Categories

None.

Contexts in which this element can be used:

As the first element in an html element.

Content model:

If the document is an iframe srcdoc document or if title information is available from a higher-level protocol: Zero or more elements of metadata content.

Otherwise: One or more elements of metadata content, of which exactly one is a title element.

Content attributes:

DOM interface:

interface HTMLHeadElement : HTMLElement {};

The head element represents a collection of metadata for the Document.

The collection of metadata in a head element can be large or small. Here is an example of a very short one:

<!doctype html>
<html>
 <head>
  <title>A document with a short head</title>
 </head>
 <body>
 ...

Here is an example of a longer one:

<!DOCTYPE HTML>
<HTML>
 <HEAD>
  <META CHARSET="UTF-8">
  <BASE HREF="http://www.example.com/">
  <TITLE>An application with a long head</TITLE>
  <LINK REL="STYLESHEET" HREF="default.css">
  <LINK REL="STYLESHEET ALTERNATE" HREF="big.css" TITLE="Big Text">
  <SCRIPT SRC="support.js"></SCRIPT>
  <META NAME="APPLICATION-NAME" CONTENT="Long headed application">
 </HEAD>
 <BODY>
 ...

The title element is a required child in most situations, but when a higher-level protocol provides title information, e.g. in the Subject line of an e-mail when HTML is used as an e-mail authoring format, the title element can be omitted.

4.2.2 The `title` element

Categories

Contexts in which this element can be used:

In a head element containing no other title elements.

Content model:

Text.

Content attributes:

DOM interface:

interface HTMLTitleElement : HTMLElement {
           attribute DOMString text;
};

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first heading, since the first heading does not have to stand alone when taken out of context.

There must be no more than one title element per document.

title . text [ = value ]

Returns the contents of the element, ignoring child nodes that aren't text nodes.

Can be set, to replace the element's children with the given value.

The IDL attribute text must return a concatenation of the contents of all the text nodes that are direct children of the title element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent IDL attribute.

Here are some examples of appropriate titles, contrasted with the top-level headings that might be used on those same pages.

  <title>Introduction to The Mating Rituals of Bees</title>
    ...
  <h1>Introduction</h1>
  <p>This companion guide to the highly successful
  <cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first heading assumes the reader knows what the context is and therefore won't wonder if the dances are Salsa or Waltz:

  <title>Dances used during bee mating rituals</title>
    ...
  <h1>The Dances</h1>

The string to use as the document's title is given by the document.title IDL attribute.

User agents should use the document's title when referring to the document in their user interface. When the contents of a title element are used in this way, the directionality of that title element should be used to set the directionality of the document's title in the user interface.

4.2.3 The `base` element

Categories

Contexts in which this element can be used:

In a head element containing no other base elements.

Content model:

Empty.

Content attributes:

href

target

DOM interface:

interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information.

There must be no more than one base element per document.

A base element must have either an href attribute, a target attribute, or both.

The href content attribute, if specified, must contain a valid URL potentially surrounded by spaces.

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn't affected by base elements).

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name or keyword, which specifies which browsing context is to be used as the default when hyperlinks and forms in the Document cause navigation.

A base element, if it has a target attribute, must come before any elements in the tree that represent hyperlinks.

If there are multiple base elements with target attributes, all but the first are ignored.

The href IDL attribute, on getting, must return the page's document base URL, and on setting, it must set the href content attribute to the given new value.

The target IDL attribute must reflect the content attribute of the same name.

In this example, a base element is used to set the document base URL:

<!DOCTYPE html>
<html>
    <head>
        <title>This is an example for the &lt;base&gt; element</title>
        <base href="http://www.example.com/news/index.html">
    </head>
    <body>
        <p>Visit the <a href="archives.html">archives</a>.</p>
    </body>
</html>

The link in the above example would be a link to "http://www.example.com/news/archives.html".

4.2.4 The `link` element

Categories

Contexts in which this element can be used:

Where metadata content is expected.

In a noscript element that is a child of a head element.

Content model:

Empty.

Content attributes:

href

rel

media

hreflang

type

sizes

Also, the title attribute has special semantics on this element.

DOM interface:

interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
  [PutForwards=value] readonly attribute DOMSettableTokenList sizes;
};
HTMLLinkElement implements LinkStyle;

The link element allows authors to link their document to other resources.

The destination of the link(s) is given by the href attribute, which must be present and must contain a valid non-empty URL potentially surrounded by spaces. If the href attribute is absent, then the element does not define a link.

A link element must have rel attribute.

The types of link indicated (the relationships) are given by the value of the rel attribute, which, if present, must have a value that is a set of space-separated tokens. The allowed keywords and their meanings are defined in a later section. If the rel attribute is absent, has no keywords, or if none of the keywords used are allowed according to the definitions in this specification, then the element does not create any links.

Two categories of links can be created using the link element: Links to external resources and hyperlinks. The link types section defines whether a particular link type is an external resource or a hyperlink. One link element can create multiple links (of which some might be external resource links and some might be hyperlinks); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

Each link created for a link element is handled separately. For instance, if there are two link elements with rel="stylesheet", they each count as a separate external resource, and each is affected by its own attributes independently. Similarly, if a single link element has a rel attribute with the value next stylesheet, it creates both a hyperlink (for the next keyword) and an external resource link (for the stylesheet keyword), and they are affected by other attributes (such as media or title) differently.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below).

For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. To obtain the resource, the user agent must run the following steps:

If the href attribute's value is the empty string, then abort these steps.
Resolve the URL given by the href attribute, relative to the element.
If the previous step fails, then abort these steps.
Fetch the resulting absolute URL.

User agents may opt to only try to obtain such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.

The semantics of the protocol used (e.g. HTTP) must be followed when fetching external resources. (For example, redirects will be followed and 404 responses will cause the external resource to not be applied.)

Once the attempts to obtain the resource and its critical subresources are complete, the user agent must, if the loads were successful, queue a task to fire a simple event named load at the link element, or, if the resource or one of its critical subresources failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), queue a task to fire a simple event named error at the link element. Non-network errors in processing the resource or its subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.

The element must delay the load event of the element's document until all the attempts to obtain the resource and its critical subresources are complete. (Resources that the user agent has not yet attempted to obtain, e.g. because it is waiting for the resource to be needed, do not delay the load event.)

Interactive user agents may provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. The exact interface is not defined by this specification, but it could include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

The relationship between this document and the resource (given by the rel attribute)
The title of the resource (given by the title attribute).
The address of the resource (given by the href attribute).
The language of the resource (given by the hreflang attribute).
The optimum media for the resource (given by the media attribute).

User agents could also include other information, such as the type of the resource (as given by the type attribute).

Hyperlinks created with the link element and its rel attribute apply to the whole page. This contrasts with the rel attribute of a and area elements, which indicates the type of a link whose context is given by the link's location within the document.

The media attribute says which media the resource applies to. The value must be a valid media query.

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must apply the external resource when the media attribute's value matches the environment and the other relevant conditions apply, and must not apply it otherwise.

The external resource might have further restrictions defined within that limit its applicability. For example, a CSS style sheet might have some @media blocks. This specification does not override such further restrictions or requirements.

The default, if the media attribute is omitted, is "all", meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on a and area elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type.

For external resource links, the type attribute is used as a hint to user agents so that they can avoid fetching resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type (even if that is not a valid MIME type, e.g. the empty string). If the attribute is omitted, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type. If the UA does not support the given MIME type for the given link relationship, then the UA should not obtain the resource; if the UA does support the given MIME type for the given link relationship, then the UA should obtain the resource at the appropriate time as specified for the external resource link's particular type. If the attribute is omitted, and the external resource link type does not have a default type defined, but the user agent would obtain the resource if the type was known and supported, then the user agent should obtain the resource under the assumption that it will be supported.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use the type attribute to determine its actual type. Only the actual type (as defined in the next paragraph) is used to determine whether to apply the resource, not the aforementioned assumed type.

If the external resource link type defines rules for processing the resource's Content-Type metadata, then those rules apply. Otherwise, if the resource is expected to be an image, user agents may apply the image sniffing rules, with the official type being the type determined from the resource's Content-Type metadata, and use the resulting sniffed type of the resource as if it was the actual type. Otherwise, if neither of these conditions apply or if the user agent opts not to apply the image sniffing rules, then the user agent must use the resource's Content-Type metadata to determine the type of the resource. If there is no type metadata, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.

The stylesheet link type defines rules for processing the resource's Content-Type metadata.

Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.

If a document contains style sheet links labeled as follows:

<link rel="stylesheet" href="A" type="text/plain">
<link rel="stylesheet" href="B" type="text/css">
<link rel="stylesheet" href="C">

...then a compliant UA that supported only CSS style sheets would fetch the B and C files, and skip the A file (since text/plain is not the MIME type for CSS style sheets).

For files B and C, it would then check the actual types returned by the server. For those that are sent as text/css, it would apply the styles, but for those labeled as text/plain, or any other type, it would not.

If one of the two files was returned without a Content-Type metadata, or with a syntactically incorrect type like Content-Type: "null", then the default type for stylesheet links would kick in. Since that default type is text/css, the style sheet would nonetheless be applied.

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternative style sheet sets.

The title attribute on link elements differs from the global title attribute of most other elements in that a link without a title does not inherit the title of the parent element: it merely has no title.

The sizes attribute is used with the icon link type. The attribute must not be specified on link elements that do not have a rel attribute that specifies the icon keyword.

HTTP Link: headers, if supported, must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. (URLs in these headers are to be processed and resolved according to the rules given in the relevant specification; the rules of this specification don't apply.) [HTTP] [WEBLINK]

The IDL attributes href, rel, media, hreflang, and type, and sizes each must reflect the respective content attributes of the same name.

The IDL attribute relList must reflect the rel content attribute.

The IDL attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternative style sheets DOM. For all other link elements it always return false and does nothing on setting.

The LinkStyle interface is also implemented by this element; the styling processing model defines how. [CSSOM]

Here, a set of link elements provide some style sheets:

<!-- a persistent style sheet -->
<link rel="stylesheet" href="default.css">

<!-- the preferred alternate style sheet -->
<link rel="stylesheet" href="green.css" title="Green styles">

<!-- some alternate style sheets -->
<link rel="alternate stylesheet" href="contrast.css" title="High contrast">
<link rel="alternate stylesheet" href="big.css" title="Big fonts">
<link rel="alternate stylesheet" href="wide.css" title="Wide screen">

The following example shows how you can specify versions of the page that use alternative formats, are aimed at other languages, and that are intended for other media:

<link rel=alternate href="/en/html" hreflang=en type=text/html title="English HTML">
<link rel=alternate href="/fr/html" hreflang=fr type=text/html title="French HTML">
<link rel=alternate href="/en/html/print" hreflang=en type=text/html media=print title="English HTML (for printing)">
<link rel=alternate href="/fr/html/print" hreflang=fr type=text/html media=print title="French HTML (for printing)">
<link rel=alternate href="/en/pdf" hreflang=en type=application/pdf title="English PDF">
<link rel=alternate href="/fr/pdf" hreflang=fr type=application/pdf title="French PDF">

4.2.5 The `meta` element

Categories

Contexts in which this element can be used:

If the charset attribute is present, or if the element's http-equiv attribute is in the Encoding declaration state: in a head element.

If the http-equiv attribute is present but not in the Encoding declaration state: in a head element.

If the http-equiv attribute is present but not in the Encoding declaration state: in a noscript element that is a child of a head element.

If the name attribute is present: where metadata content is expected.

Content model:

Empty.

Content attributes:

name

http-equiv

content

charset

DOM interface:

interface HTMLMetaElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString httpEquiv;
           attribute DOMString content;
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, and charset attributes must be specified.

If either name or http-equiv is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute specifies the character encoding used by the document. This is a character encoding declaration. If the attribute is present in an XML document, its value must be an ASCII case-insensitive match for the string "UTF-8" (and the document is therefore forced to use UTF-8 as its encoding).

The charset attribute on the meta element has no effect in XML documents, and is only allowed in order to facilitate migration to and from XHTML.

There must not be more than one meta element with a charset attribute per document.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name/value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

The name and content IDL attributes must reflect the respective content attributes of the same name. The IDL attribute httpEquiv must reflect the content attribute http-equiv.

4.2.5.1 Standard metadata names

This specification defines a few names for the name attribute of the meta element.

Names are case-insensitive, and must be compared in an ASCII case-insensitive manner.

application-name

The value must be a short free-form string giving the name of the Web application that the page represents. If the page is not a Web application, the application-name metadata name must not be used. There must not be more than one meta element with its name attribute set to the value application-name per document. User agents may use the application name in UI in preference to the page's title, since the title might include status messages and the like relevant to the status of the page at a particular moment in time instead of just being the name of the application.

author

The value must be a free-form string giving the name of one of the page's authors.

description

The value must be a free-form string that describes the page. The value must be appropriate for use in a directory of pages, e.g. in a search engine. There must not be more than one meta element with its name attribute set to the value description per document.

generator

The value must be a free-form string that identifies one of the software packages used to generate the document. This value must not be used on hand-authored pages.

Here is what a tool called "Frontweaver" could include in its output, in the page's head element, to identify itself as the tool used to generate the page:

<meta name=generator content="Frontweaver 8.2">

keywords

The value must be a set of comma-separated tokens, each of which is a keyword relevant to the page.

This page about typefaces on British motorways uses a meta element to specify some keywords that users might use to look for the page:

<!DOCTYPE HTML>
<html>
 <head>
  <title>Typefaces on UK motorways</title>
  <meta name="keywords" content="british,type face,font,fonts,highway,highways">
 </head>
 <body>
  ...

Many search engines do not consider such keywords, because this feature has historically been used unreliably and even misleadingly as a way to spam search engine results in a way that is not helpful for users.

To obtain the list of keywords that the author has specified as applicable to the page, the user agent must run the following steps:

Let keywords be an empty list.
For each meta element with a name attribute and a content attribute and whose name attribute's value is keywords, run the following substeps:
1. Split the value of the element's content attribute on commas.
2. Add the resulting tokens, if any, to keywords.
Remove any duplicates from keywords.
Return keywords. This is the list of keywords that the author has specified as applicable to the page.

User agents should not use this information when there is insufficient confidence in the reliability of the value.

For instance, it would be reasonable for a content management system to use the keyword information of pages within the system to populate the index of a site-specific search engine, but a large-scale content aggregator that used this information would likely find that certain users would try to game its ranking mechanism through the use of inappropriate keywords.

4.2.5.2 Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page. [WHATWGWIKI]

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short non-normative description of what the metadata name's meaning is, including the format the value is required to be in.

Specification

A link to a more detailed description of the metadata name's semantics and requirements. It could be another page on the Wiki, or a link to an external page.

Synonyms

A list of other names that have exactly the same processing requirements. Authors should not use the names defined to be synonyms, they are only intended to allow user agents to support legacy content. Anyone may remove synonyms that are not used in practice; only names that need to be processed as synonyms for compatibility with legacy content are to be registered in this way.

Status

One of the following:

Proposed: The name has not received wide peer review and approval. Someone has proposed it and is, or soon will be, using it.
Ratified: The name has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the name, including when they use it in incorrect ways.
Discontinued: The metadata name has received wide peer review and it has been found wanting. Existing pages are using this metadata name, but new pages should avoid it. The "brief description" and "specification" entries will give details of what authors should use instead, if anything.

If a metadata name is found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

If a metadata name is registered in the "proposed" state for a period of a month or more without being used or specified, then it may be removed from the registry.

If a metadata name is added with the "proposed" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value. If a metadata name is added with the "proposed" status and found to be harmful, then it should be changed to "discontinued" status.

Anyone can change the status at any time, but should only do so in accordance with the definitions above.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value is allowed or not: values defined in this specification or marked as "proposed" or "ratified" must be accepted, whereas values marked as "discontinued" or not listed in either this specification or on the aforementioned page must be rejected as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).

When an author uses a new metadata name not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposed" status.

Metadata names whose values are to be URLs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

4.2.5.3 Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map. Some of the keywords are non-conforming, as noted in the last column.

State	Keyword	Notes
Content Language	`content-language`	Non-conforming
Encoding declaration	`content-type`
Default style	`default-style`
Refresh	`refresh`
Cookie setter	`set-cookie`	Non-conforming

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Content language state (http-equiv="content-language")

This feature is non-conforming. Authors are encouraged to use the lang attribute instead.

This pragma sets the pragma-set default language. Until the pragma is successfully processed, there is no pragma-set default language.

If another meta element with an http-equiv attribute in the Content Language state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.
If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
If the element's content attribute contains a U+002C COMMA character (,) then abort these steps.
Let input be the value of the element's content attribute.
Let position point at the first character of input.
Skip whitespace.
Collect a sequence of characters that are not space characters.
Let the pragma-set default language be the string that resulted from the previous step.

This pragma is not exactly equivalent to the HTTP Content-Language header. [HTTP]

Encoding declaration state (http-equiv="content-type")

The Encoding declaration state is just an alternative form of setting the charset attribute: it is a character encoding declaration. This state's user agent requirements are all handled by the parsing section of the specification.

For meta elements with an http-equiv attribute in the Encoding declaration state, the content attribute must have a value that is an ASCII case-insensitive match for a string that consists of: the literal string "text/html;", optionally followed by any number of space characters, followed by the literal string "charset=", followed by the character encoding name of the character encoding declaration.

A document must not contain both a meta element with an http-equiv attribute in the Encoding declaration state and a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents, but elements with an http-equiv attribute in that state must not be used in XML documents.

Default style state (http-equiv="default-style")

This pragma sets the name of the default alternative style sheet set.

If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
Set the preferred style sheet set to the value of the element's content attribute. [CSSOM]

Refresh state (http-equiv="refresh")

This pragma acts as timed redirect.

If another meta element with an http-equiv attribute in the Refresh state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.
If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
Let input be the value of the element's content attribute.
Let position point at the first character of input.
Skip whitespace.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and parse the resulting string using the rules for parsing non-negative integers. If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. Otherwise, let time be the parsed number.
Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) and U+002E FULL STOP (.). Ignore any collected characters.
Skip whitespace.
Let url be the address of the current page.
If the character in input pointed to by position is a U+003B SEMICOLON (";"), then advance position to the next character. Otherwise, jump to the last step.
Skip whitespace.
If the character in input pointed to by position is a U+0055 LATIN CAPITAL LETTER U character (U) or a U+0075 LATIN SMALL LETTER U character (u), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is a U+0052 LATIN CAPITAL LETTER R character (R) or a U+0072 LATIN SMALL LETTER R character (r), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is s U+004C LATIN CAPITAL LETTER L character (L) or a U+006C LATIN SMALL LETTER L character (l), then advance position to the next character. Otherwise, jump to the last step.
Skip whitespace.
If the character in input pointed to by position is a U+003D EQUALS SIGN ("="), then advance position to the next character. Otherwise, jump to the last step.
Skip whitespace.
If the character in input pointed to by position is either a U+0027 APOSTROPHE character (') or U+0022 QUOTATION MARK character ("), then let quote be that character, and advance position to the next character. Otherwise, let quote be the empty string.
Let url be equal to the substring of input from the character at position to the end of the string.
If quote is not the empty string, and there is a character in url equal to quote, then truncate url at that character, so that it and all subsequent characters are removed.
Strip any trailing space characters from the end of url.
Strip any U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.
Resolve the url value to an absolute URL, relative to the meta element. If this fails, abort these steps.
Perform one or more of the following steps:
- After the refresh has come due (as defined below), if the user has not canceled the redirect and if the meta element's Document's browsing context did not have the sandboxed automatic features browsing context flag set when the Document was created, navigate the Document's browsing context to url, with replacement enabled, and with the Document's browsing context as the source browsing context.
  
  For the purposes of the previous paragraph, a refresh is said to have come due as soon as the later of the following two conditions occurs:
  - At least time seconds have elapsed since the document has completely loaded, adjusted to take into account user or user agent preferences.
  - At least time seconds have elapsed since the meta element was inserted into the Document, adjusted to take into account user or user agent preferences.
- Provide the user with an interface that, when selected, navigates a browsing context to url, with the document's browsing context as the source browsing context.
- Do nothing.
In addition, the user agent may, as with anything, inform the user of any and all aspects of its operation, including the state of any timers, the destinations of any timed redirects, and so forth.

For meta elements with an http-equiv attribute in the Refresh state, the content attribute must have a value consisting either of:

just a valid non-negative integer, or
a valid non-negative integer, followed by a U+003B SEMICOLON character (;), followed by one or more space characters, followed by a substring that is an ASCII case-insensitive match for the string "URL", followed by a U+003D EQUALS SIGN character (=), followed by a valid URL that does not start with a literal U+0027 APOSTROPHE (') or U+0022 QUOTATION MARK (") character.

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URL.

A news organization's front page could include the following markup in the page's head element, to ensure that the page automatically reloads from the server every five minutes:

<meta http-equiv="Refresh" content="300">

A sequence of pages could be used as an automated slide show by making each page refresh to the next page in the sequence, using markup such as the following:

<meta http-equiv="Refresh" content="20; URL=page4.html">

Cookie setter (http-equiv="set-cookie")

This pragma sets an HTTP cookie. [COOKIES]

It is non-conforming. Real HTTP headers should be used instead.

If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
Obtain the storage mutex.
Act as if receiving a set-cookie-string for the document's address via a "non-HTTP" API, consisting of the value of the element's content attribute encoded as UTF-8. [COOKIES] [RFC3629]

There must not be more than one meta element with any particular state in the document at a time.

4.2.5.4 Other pragma directives

Extensions to the predefined set of pragma directives may, under certain conditions, be registered in the WHATWG Wiki PragmaExtensions page. [WHATWGWIKI]

Such extensions must use a name that is identical to an HTTP header registered in the Permanent Message Header Field Registry, and must have behavior identical to that described for the HTTP header. [IANAPERMHEADERS]

Pragma directives corresponding to headers describing metadata, or not requiring specific user agent processing, must not be registered; instead, use metadata names. Pragma directives corresponding to headers that affect the HTTP processing model (e.g. caching) must not be registered, as they would result in HTTP-level behavior being different for user agents that implement HTML than for user agents that do not.

Anyone is free to edit the WHATWG Wiki PragmaExtensions page at any time to add a pragma directive satisfying these conditions. Such registrations must specify the following information:

Keyword: The actual name being defined. The name must match a previously-registered HTTP name with the same requirements.
Brief description: A short non-normative description of the purpose of the pragma directive.
Specification: A link to the specification defining the corresponding HTTP header.

Conformance checkers must use the information given on the WHATWG Wiki PragmaExtensions page to establish if a value is allowed or not: values defined in this specification or listed on the aforementioned page must be accepted, whereas values not listed in either this specification or on the aforementioned page must be rejected as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).

4.2.5.5 Specifying the document's character encoding

A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.

The following restrictions apply to character encoding declarations:

The character encoding name given must be the name of the character encoding used to serialize the file.
The value must be a valid character encoding name, and must be an ASCII case-insensitive match for the preferred MIME name for that encoding. [IANACHARSET]
The character encoding declaration must be serialized without the use of character references or character escapes of any kind.
The element containing the character encoding declaration must be serialized completely within the first 1024 bytes of the document.

In addition, due to a number of restrictions on meta elements, there can only be one meta-based character encoding declaration per document.

If an HTML document does not start with a BOM, and if its encoding is not explicitly given by Content-Type metadata, and the document is not an iframe srcdoc document, then the character encoding used must be an ASCII-compatible character encoding, and, in addition, if that encoding isn't US-ASCII itself, then the encoding must be specified using a meta element with a charset attribute or a meta element with an http-equiv attribute in the Encoding declaration state.

If the document is an iframe srcdoc document, the document must not have a character encoding declaration. (In this case, the source is already decoded, since it is part of the document that contained the iframe.)

If an HTML document contains a meta element with a charset attribute or a meta element with an http-equiv attribute in the Encoding declaration state, then the character encoding used must be an ASCII-compatible character encoding.

Authors are encouraged to use UTF-8. Conformance checkers may advise authors against using legacy encodings. [RFC3629]

Authoring tools should default to using UTF-8 for newly-created documents. [RFC3629]

Encodings in which a series of bytes in the range 0x20 to 0x7E can encode characters other than the corresponding characters in the range U+0020 to U+007E represent a potential security vulnerability: a user agent that does not support the encoding (or does not support the label used to declare the encoding, or does not use the same mechanism to detect the encoding of unlabelled content as another user agent) might end up interpreting technically benign plain text content as HTML tags and JavaScript. For example, this applies to encodings in which the bytes corresponding to "<script>" in ASCII can encode a different string. Authors should not use such encodings, which are known to include JIS_C6226-1983, JIS_X0212-1990, HZ-GB-2312, JOHAB (Windows code page 1361), encodings based on ISO-2022, and encodings based on EBCDIC. Furthermore, authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings, which also fall into this category, because these encodings were never intended for use for Web content. [RFC1345] [RFC1842] [RFC1468] [RFC2237] [RFC1554] [RFC1922] [RFC1557] [CESU8] [UTF7] [BOCU1] [SCSU]

Authors should not use UTF-32, as the encoding detection algorithms described in this specification intentionally do not distinguish it from UTF-16. [UNICODE]

Using non-UTF-8 encodings can have unexpected results on form submission and URL encodings, which use the document's character encoding by default.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

In HTML, to declare that the character encoding is UTF-8, the author could include the following markup near the top of the document (in the head element):

<meta charset="utf-8">

In XML, the XML declaration would be used instead, at the very top of the markup:

<?xml version="1.0" encoding="utf-8"?>

4.2.6 The `style` element

Categories

If the scoped attribute is present: flow content.

Contexts in which this element can be used:

If the scoped attribute is absent: where metadata content is expected.

If the scoped attribute is absent: in a noscript element that is a child of a head element.

If the scoped attribute is present: where flow content is expected, but before any other flow content other than other style elements and inter-element whitespace.

Content model:

Depends on the value of the type attribute, but must match requirements described in prose below.

Content attributes:

media

type

scoped

Also, the title attribute has special semantics on this element.

DOM interface:

interface HTMLStyleElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString media;
           attribute DOMString type;
           attribute boolean scoped;
};
HTMLStyleElement implements LinkStyle;

The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model. The element does not represent content for the user.

The type attribute gives the styling language. If the attribute is present, its value must be a valid MIME type that designates a styling language. The charset parameter must not be specified. The default value for the type attribute, which is used if the attribute is absent, is "text/css". [RFC2318]

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported. The charset parameter must be treated as an unknown parameter for the purpose of comparing MIME types here.

The media attribute says which media the styles apply to. The value must be a valid media query. The user agent must apply the styles when the media attribute's value matches the environment and the other relevant conditions apply, and must not apply them otherwise.

The styles might be further limited in scope, e.g. in CSS with the use of @media blocks. This specification does not override such further restrictions or requirements.

The default, if the media attribute is omitted, is "all", meaning that by default styles apply to all media.

The scoped attribute is a boolean attribute. If set, it indicates that the styles are intended just for the subtree rooted at the style element's parent element, as opposed to the whole Document.

If the scoped attribute is present, then the user agent must apply the specified style information only to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

For scoped CSS resources, the effect of @-rules must be scoped to the scoped sheet and its subresources, even if the @-rule in question would ordinarily apply to all style sheets that affect the Document. Any '@page' rules in scoped CSS resources must be ignored.

For example, an '@font-face' rule defined in a scoped style sheet would only define the font for the purposes of font rules in the scoped section; style sheets outside the scoped section using the same font name would not end up using that embedded font.

The title attribute on style elements defines alternative style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element. [CSSOM]

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

The textContent of a style element must match the style production in the following ABNF, the character set for which is Unicode. [ABNF]

style         = no-c-start *( c-start no-c-end c-end no-c-start )
no-c-start    = <any string that doesn't contain a substring that matches c-start >
c-start       = "<!--"
no-c-end      = <any string that doesn't contain a substring that matches c-end >
c-end         = "-->"

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text (as opposed to XML), user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the child nodes of the style element to the style system.

All URLs found by the styling language's processor must be resolved, relative to the element (or as defined by the styling language), when the processor is invoked.

Once the attempts to obtain the style sheet's critical subresources, if any, are complete, or, if the style sheet has no critical subresources, once the style sheet has been parsed and processed, the user agent must, if the loads were successful or there were none, queue a task to fire a simple event named load at the style element, or, if one of the style sheet's critical subresources failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), queue a task to fire a simple event named error at the style element. Non-network errors in processing the style sheet or its subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.

The element must delay the load event of the element's document until all the attempts to obtain the style sheet's critical subresources, if any, are complete.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS]

The media, type and scoped IDL attributes must reflect the respective content attributes of the same name.

The disabled IDL attribute behaves as defined for the alternative style sheets DOM.

The LinkStyle interface is also implemented by this element; the styling processing model defines how. [CSSOM]

The following document has its emphasis styled as bright red text rather than italics text, while leaving titles of works and Latin words in their default italics. It shows how using appropriate elements enables easier restyling of documents.

<!DOCTYPE html>
<html lang="en-US">
 <head>
  <title>My favorite book</title>
  <style>
   body { color: black; background: white; }
   em { font-style: normal; color: red; }
  </style>
 </head>
 <body>
  <p>My <em>favorite</em> book of all time has <em>got</em> to be
  <cite>A Cat's Life</cite>. It is a book by P. Rahmel that talks
  about the <i lang="la">Felis Catus</i> in modern human society.</p>
 </body>
</html>

4.2.7 Styling

The link and style elements can provide styling information for the user agent to use when rendering the document. The DOM Styling specification specifies what styling information is to be used by the user agent and how it is to be used. [CSSOM]

The style and link elements implement the LinkStyle interface. [CSSOM]

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been fetched, or is not in a supported styling language, must have their LinkStyle interface's sheet attribute return null.

Otherwise, the LinkStyle interface's sheet attribute must return a StyleSheet object with the following properties: [CSSOM]

The style sheet type: The style sheet type must be the same as the style's specified type. For style elements, this is the same as the type content attribute's value, or text/css if that is omitted. For link elements, this is the Content-Type metadata of the specified resource.
The style sheet location: For link elements, the location must be the result of resolving the URL given by the element's href content attribute, relative to the element, or the empty string if that fails. For style elements, there is no location.
The style sheet media: The media must be the same as the value of the element's media content attribute, or the empty string, if the attribute is omitted.
The style sheet title: The title must be the same as the value of the element's title content attribute, if the attribute is present and has a non-empty value. If the attribute is absent or its value is the empty string, then the style sheet does not have a title (it is the empty string). The title is used for defining alternative style sheet sets.
The style sheet alternate flag: For link elements, true if the link is an alternative stylesheet. In all other cases, false.

The same object must be returned each time.

The disabled IDL attribute on link and style elements must return false and do nothing on setting, if the sheet attribute of their LinkStyle interface is null. Otherwise, it must return the value of the StyleSheet interface's disabled attribute on getting, and forward the new value to that same attribute on setting.

The rules for handling alternative style sheets are defined in the CSS object model specification. [CSSOM]

Style sheets, whether added by a link element, a style element, an <?xml-stylesheet> PI, an HTTP Link: header, or some other mechanism, have a style sheet ready flag, which is initially unset.

When a style sheet is ready to be applied, its style sheet ready flag must be set. If the style sheet referenced no other resources (e.g. it was an internal style sheet given by a style element with no @import rules), then the style rules must be synchronously made available to script; otherwise, the style rules must only be made available to script once the event loop reaches its "update the rendering" step.

A style sheet in the context of the Document of an HTML parser or XML parser is said to be a style sheet that is blocking scripts if the element was created by that Document's parser, and the element is either a style element or a link element that was an external resource link that contributes to the styling processing model when the element was created by the parser, and the element's style sheet was enabled when the element was created by the parser, and the element's style sheet ready flag is not yet set, and, the last time the event loop reached step 1, the element was in that Document, and the user agent hasn't given up on that particular style sheet yet. A user agent may give up on a style sheet at any time.

A Document has a style sheet that is blocking scripts if there is either a style sheet that is blocking scripts in the context of that Document, or if that Document is in a browsing context that has a parent browsing context, and the active document of that parent browsing context itself has a style sheet that is blocking scripts.

A Document has no style sheet that is blocking scripts if it does not have a style sheet that is blocking scripts as defined in the previous paragraph.

4.3 Scripting

Scripts allow authors to add interactivity to their documents.

Authors are encouraged to use declarative alternatives to scripting where possible, as declarative mechanisms are often more maintainable, and many users disable scripting.

For example, instead of using script to show or hide a section to show more details, the details element could be used.

Authors are also encouraged to make their applications degrade gracefully in the absence of scripting support.

For example, if an author provides a link in a table header to dynamically resort the table, the link could also be made to function without scripts by requesting the sorted table from the server.

4.3.1 The `script` element

Categories

Contexts in which this element can be used:

Where metadata content is expected.

Where phrasing content is expected.

Content model:

If there is no src attribute, depends on the value of the type attribute, but must match script content restrictions.

If there is a src attribute, the element must be either empty or contain only script documentation that also matches script content restrictions.

Content attributes:

src

async

defer

type

charset

DOM interface:

interface HTMLScriptElement : HTMLElement {
           attribute DOMString src;
           attribute boolean async;
           attribute boolean defer;
           attribute DOMString type;
           attribute DOMString charset;
           attribute DOMString text;
};

The script element allows authors to include dynamic script and data blocks in their documents. The element does not represent content for the user.

When used to include dynamic scripts, the scripts may either be embedded inline or may be imported from an external file using the src attribute. If the language is not that described by "text/javascript", then the type attribute must be present, as described below. Whatever language is used, the contents of the script element must conform with the requirements of that language's specification.

When used to include data blocks (as opposed to scripts), the data must be embedded inline, the format of the data must be given using the type attribute, the src attribute must not be specified, and the contents of the script element must conform to the requirements defined for the format used.

The type attribute gives the language of the script or format of the data. If the attribute is present, its value must be a valid MIME type. The charset parameter must not be specified. The default, which is used if the attribute is absent, is "text/javascript".

The src attribute, if specified, gives the address of the external script resource to use. The value of the attribute must be a valid non-empty URL potentially surrounded by spaces identifying a script resource of the type given by the type attribute, if the attribute is present, or of the type "text/javascript", if the attribute is absent. A resource is a script resource of a given type if that type identifies a scripting language and the resource conforms with the requirements of that language's specification.

The charset attribute gives the character encoding of the external script resource. The attribute must not be specified if the src attribute is not present. If the attribute is set, its value must be a valid character encoding name, must be an ASCII case-insensitive match for the preferred MIME name for that encoding, and must match the encoding given in the charset parameter of the Content-Type metadata of the external file, if any. [IANACHARSET]

The async and defer attributes are boolean attributes that indicate how the script should be executed. The defer and async attributes must not be specified if the src attribute is not present.

There are three possible modes that can be selected using these attributes. If the async attribute is present, then the script will be executed asynchronously, as soon as it is available. If the async attribute is not present but the defer attribute is present, then the script is executed when the page has finished parsing. If neither attribute is present, then the script is fetched and executed immediately, before the user agent continues parsing the page.

The exact processing details for these attributes are, for mostly historical reasons, somewhat non-trivial, involving a number of aspects of HTML. The implementation requirements are therefore by necessity scattered throughout the specification. The algorithms below (in this section) describe the core of this processing, but these algorithms reference and are referenced by the parsing rules for script start and end tags in HTML, in foreign content, and in XML, the rules for the document.write() method, the handling of scripting, etc.

The defer attribute may be specified even if the async attribute is specified, to cause legacy Web browsers that only support defer (and not async) to fall back to the defer behavior instead of the synchronous blocking behavior that is the default.

Changing the src, type, charset, async, and defer attributes dynamically has no direct effect; these attribute are only used at specific times described below.

A script element has several associated pieces of state.

The first is a flag indicating whether or not the script block has been "already started". Initially, script elements must have this flag unset (script blocks, when created, are not "already started"). When a script element is cloned, the "already started" flag, if set, must be propagated to the clone when it is created.

The second is a flag indicating whether the element was "parser-inserted". Initially, script elements must have this flag unset. It is set by the HTML parser and the XML parser on script elements they insert and affects the processing of those elements.

The third is a flag indicating whether the element will "force-async". Initially, script elements must have this flag set. It is unset by the HTML parser and the XML parser on script elements they insert. In addition, whenever a script element whose "force-async" flag is set has a async content attribute added, the element's "force-async" flag must be unset.

The fourth is a flag indicating whether or not the script block is "ready to be parser-executed". Initially, script elements must have this flag unset (script blocks, when created, are not "ready to be parser-executed"). This flag is used only for elements that are also "parser-inserted", to let the parser know when to execute the script.

The last few pieces of state are the script block's type, the script block's character encoding, and the script block's fallback character encoding. They are determined when the script is prepared, based on the attributes on the element at that time, and the Document of the script element.

When a script element that is not marked as being "parser-inserted" experiences one of the events listed in the following list, the user agent must synchronously prepare the script element:

The script element gets inserted into a document.
The script element is in a Document and its child nodes are changed.
The script element is in a Document and has a src attribute set where previously the element had no such attribute.

To prepare a script, the user agent must act as follows:

If the script element is marked as having "already started", then the user agent must abort these steps at this point. The script is not executed.
If the element has its "parser-inserted" flag set, then set was-parser-inserted to true and unset the element's "parser-inserted" flag. Otherwise, set was-parser-inserted to false.

This is done so that if parser-inserted script elements fail to run when the parser tries to run them, e.g. because they are empty or specify an unsupported scripting language, another script can later mutate them and cause them to run again.
If was-parser-inserted is true and the element does not have an async attribute, then set the element's "force-async" flag to true.

This is done so that if a parser-inserted script element fails to run when the parser tries to run it, but it is later executed after a script dynamically updates it, it will execute asynchronously even if the async attribute isn't set.
If the element has no src attribute, and its child nodes, if any, consist only of comment nodes and empty text nodes, then the user agent must abort these steps at this point. The script is not executed.
If the element is not in a Document, then the user agent must abort these steps at this point. The script is not executed.
If either:
- the script element has a type attribute and its value is the empty string, or
- the script element has no type attribute but it has a language attribute and that attribute's value is the empty string, or
- the script element has neither a type attribute nor a language attribute, then
...let the script block's type for this script element be "text/javascript".

Otherwise, if the script element has a type attribute, let the script block's type for this script element be the value of that attribute with any leading or trailing sequences of space characters removed.

Otherwise, the element has a non-empty language attribute; let the script block's type for this script element be the concatenation of the string "text/" followed by the value of the language attribute.

The language attribute is never conforming, and is always ignored if there is a type attribute present.
If the user agent does not support the scripting language given by the script block's type for this script element, then the user agent must abort these steps at this point. The script is not executed.
If was-parser-inserted is true, then flag the element as "parser-inserted" again, and set the element's "force-async" flag to false.
The user agent must set the element's "already started" flag.

The state of the element at this moment is later used to determine the script source.
If the element is flagged as "parser-inserted", but the element's Document is not the Document of the parser that created the element, then abort these steps.
If scripting is disabled for the script element, then the user agent must abort these steps at this point. The script is not executed.

The definition of scripting is disabled means that, amongst others, the following scripts will not execute: scripts in XMLHttpRequest's responseXML documents, scripts in DOMParser-created documents, scripts in documents created by XSLTProcessor's transformToDocument feature, and scripts that are first inserted by a script into a Document that was created using the createDocument() API. [XHR] [DOMPARSER] [DOMCORE]
If the script element has an event attribute and a for attribute, then run these substeps:
1. Let for be the value of the for attribute.
2. Let event be the value of the event attribute.
3. Strip leading and trailing whitespace from event and for.
4. If for is not an ASCII case-insensitive match for the string "window", then the user agent must abort these steps at this point. The script is not executed.
5. If event is not an ASCII case-insensitive match for either the string "onload" or the string "onload()", then the user agent must abort these steps at this point. The script is not executed.
If the script element has a charset attribute, then let the script block's character encoding for this script element be the encoding given by the charset attribute.

Otherwise, let the script block's fallback character encoding for this script element be the same as the encoding of the document itself.

Only one of these two pieces of state is set.
If the element has a src attribute whose value is not the empty string, then the value of that attribute must be resolved relative to the element, and if that is successful, the specified resource must then be fetched, from the origin of the element's Document.

If the src attribute's value is the empty string or if it could not be resolved, then the user agent must queue a task to fire a simple event named error at the element, and abort these steps.

For historical reasons, if the URL is a javascript: URL, then the user agent must not, despite the requirements in the definition of the fetching algorithm, actually execute the script in the URL; instead the user agent must act as if it had received an empty HTTP 400 response.

For performance reasons, user agents may start fetching the script as soon as the attribute is set, instead, in the hope that the element will be inserted into the document. Either way, once the element is inserted into the document, the load must have started. If the UA performs such prefetching, but the element is never inserted in the document, or the src attribute is dynamically changed, then the user agent will not execute the script, and the fetching process will have been effectively wasted.
Then, the first of the following options that describes the situation must be followed:
If the element has a src attribute, and the element has a defer attribute, and the element has been flagged as "parser-inserted", and the element does not have an async attribute

The element must be added to the end of the list of scripts that will execute when the document has finished parsing associated with the Document of the parser that created the element.

The task that the networking task source places on the task queue once the fetching algorithm has completed must set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

If the element has a src attribute, and the element has been flagged as "parser-inserted", and the element does not have an async attribute

The element is the pending parsing-blocking script of the Document of the parser that created the element. (There can only be one such script per Document at a time.)

The task that the networking task source places on the task queue once the fetching algorithm has completed must set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

If the element does not have a src attribute, and the element has been flagged as "parser-inserted", and the Document of the HTML parser or XML parser that created the script element has a style sheet that is blocking scripts

The element is the pending parsing-blocking script of the Document of the parser that created the element. (There can only be one such script per Document at a time.)

Set the element's "ready to be parser-executed" flag. The parser will handle executing the script.

If the element has a src attribute, does not have an async attribute, and does not have the "force-async" flag set
The element must be added to the end of the list of scripts that will execute in order as soon as possible associated with the Document of the script element at the time the prepare a script algorithm started.

The task that the networking task source places on the task queue once the fetching algorithm has completed must run the following steps:
1. If the element is not now the first element in the list of scripts that will execute in order as soon as possible to which it was added above, then mark the element as ready but abort these steps without executing the script yet.
2. Execution: Execute the script block corresponding to the first script element in this list of scripts that will execute in order as soon as possible.
3. Remove the first element from this list of scripts that will execute in order as soon as possible.
4. If this list of scripts that will execute in order as soon as possible is still not empty and the first entry has already been marked as ready, then jump back to the step labeled execution.
If the element has a src attribute

The element must be added to the set of scripts that will execute as soon as possible of the Document of the script element at the time the prepare a script algorithm started.

The task that the networking task source places on the task queue once the fetching algorithm has completed must execute the script block and then remove the element from the set of scripts that will execute as soon as possible.

Otherwise

The user agent must immediately execute the script block, even if other scripts are already executing.

Fetching an external script must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined above) has been run.

The pending parsing-blocking script of a Document is used by the Document's parser(s).

If a script element that blocks a parser gets moved to another Document before it would normally have stopped blocking that parser, it nonetheless continues blocking that parser until the condition that causes it to be blocking the parser no longer applies (e.g. if the script is a pending parsing-blocking script because there was a style sheet that is blocking scripts when it was parsed, but then the script is moved to another Document before the style sheet loads, the script still blocks the parser until the style sheets are all loaded, at which time the script executes and the parser is unblocked).

When the user agent is required to execute a script block, it must run the following steps:

If the element is flagged as "parser-inserted", but the element's Document is not the Document of the parser that created the element, then abort these steps.

Jump to the appropriate set of steps from the list below:

If the load resulted in an error (for example a DNS error, or an HTTP 404 error)

Executing the script block must just consist of firing a simple event named error at the element.

If the load was successful

Executing the script block must consist of running the following steps. For the purposes of these steps, the script is considered to be from an external file if, while the prepare a script algorithm above was running for this script, the script element had a src attribute specified.

Initialize the script block's source as follows:

If the script is from an external file and the script block's type is a text-based language

The contents of that file, interpreted as string of Unicode characters, are the script source.

To obtain the string of Unicode characters, the user agent run the following steps:

If the resource's Content Type metadata, if any, specifies a character encoding, and the user agent supports that encoding, then let character encoding be that encoding, and jump to the bottom step in this series of steps.
If the algorithm above set the script block's character encoding, then let character encoding be that encoding, and jump to the bottom step in this series of steps.

For each of the rows in the following table, starting with the first one and going down, if the file has as many or more bytes available than the number of bytes in the first column, and the first bytes of the file match the bytes given in the first column, then set character encoding to the encoding given in the cell in the second column of that row, and jump to the bottom step in this series of steps:

Bytes in Hexadecimal	Encoding
FE FF	Big-endian UTF-16
FF FE	Little-endian UTF-16
EF BB BF	UTF-8

This step looks for Unicode Byte Order Marks (BOMs).

Let character encoding be the script block's fallback character encoding.
Convert the file to Unicode using character encoding, following the rules for doing so given by the specification for the script block's type.

If the script is from an external file and the script block's type is an XML-based language

The external file is the script source. When it is later executed, it must be interpreted in a manner consistent with the specification defining the language given by the script block's type.

If the script is inline and the script block's type is a text-based language

The value of the text IDL attribute at the time the element's "already started" flag was last set is the script source.

If the script is inline and the script block's type is an XML-based language

The child nodes of the script element at the time the element's "already started" flag was last set are the script source.

If the script is from an external file, then increment the ignore-destructive-writes counter of the script element's Document. Let neutralized doc be that Document.
Create a script from the script element node, using the script block's source and the script block's type.

This is where the script is compiled and actually executed.
Decrement the ignore-destructive-writes counter of neutralized doc, if it was incremented in the earlier step.
If the script is from an external file, fire a simple event named load at the script element.

Otherwise, the script is internal; queue a task to fire a simple event named load at the script element.

The IDL attributes src, type, charset, and defer, each must reflect the respective content attributes of the same name.

The async IDL attribute controls whether the element will execute asynchronously or not. If the element's "force-async" flag is set, then, on getting, the async IDL attribute must return true, and on setting, the "force-async" flag must first be unset, and then the content attribute must be removed if the IDL attribute's new value is false, and must be set to the empty string if the IDL attribute's new value is true. If the element's "force-async" flag is not set, the IDL attribute must reflect the async content attribute.

script . text [ = value ]

Returns the contents of the element, ignoring child nodes that aren't text nodes.

Can be set, to replace the element's children with the given value.

The IDL attribute text must return a concatenation of the contents of all the text nodes that are direct children of the script element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent IDL attribute.

When inserted using the document.write() method, script elements execute (typically synchronously), but when inserted using innerHTML and outerHTML attributes, they do not execute at all.

In this example, two script elements are used. One embeds an external script, and the other includes some data.

<script src="game-engine.js"></script>
<script type="text/x-game-map">
........U.........e
o............A....e
.....A.....AAA....e
.A..AAA...AAAAA...e
</script>

The data in this case might be used by the script to generate the map of a video game. The data doesn't have to be used that way, though; maybe the map data is actually embedded in other parts of the page's markup, and the data block here is just used by the site's search engine to help users who are looking for particular features in their game maps.

The following sample shows how a script element can be used to define a function that is then used by other parts of the document. It also shows how a script element can be used to invoke script while the document is being parsed, in this case to initialize the form's output.

<script>
 function calculate(form) {
   var price = 52000;
   if (form.elements.brakes.checked)
     price += 1000;
   if (form.elements.radio.checked)
     price += 2500;
   if (form.elements.turbo.checked)
     price += 5000;
   if (form.elements.sticker.checked)
     price += 250;
   form.elements.result.value = price;
 }
</script>
<form name="pricecalc" onsubmit="return false" onchange="calculate(this)">
 <fieldset>
  <legend>Work out the price of your car</legend>
  <p>Base cost: £52000.</p>
  <p>Select additional options:</p>
  <ul>
   <li><label><input type=checkbox name=brakes> Ceramic brakes (£1000)</label></li>
   <li><label><input type=checkbox name=radio> Satellite radio (£2500)</label></li>
   <li><label><input type=checkbox name=turbo> Turbo charger (£5000)</label></li>
   <li><label><input type=checkbox name=sticker> "XZ" sticker (£250)</label></li>
  </ul>
  <p>Total: £<output name=result></output></p>
 </fieldset>
 <script>
  calculate(document.forms.pricecalc);
 </script>
</form>

4.3.1.1 Scripting languages

A user agent is said to support the scripting language if the script block's type is an ASCII case-insensitive match for the MIME type string of a scripting language that the user agent implements.

The following lists some MIME type strings and the languages to which they refer:

"application/ecmascript"
"application/javascript"
"application/x-ecmascript"
"application/x-javascript"
"text/ecmascript"
"text/javascript"
"text/javascript1.0"
"text/javascript1.1"
"text/javascript1.2"
"text/javascript1.3"
"text/javascript1.4"
"text/javascript1.5"
"text/jscript"
"text/livescript"
"text/x-ecmascript"
"text/x-javascript": JavaScript. [ECMA262]
"text/javascript;e4x=1": JavaScript with ECMAScript for XML. [ECMA357]

User agents may support other MIME types and other languages.

4.3.1.2 Restrictions for contents of `script` elements

The textContent of a script element must match the script production in the following ABNF, the character set for which is Unicode. [ABNF]

script        = data1 *( escape [ script-start data3 ] "-->" data1 ) [ escape ]
escape        = "<!--" data2 *( script-start data3 script-end data2 )

data1         = <any string that doesn't contain a substring that matches not-data1>
not-data1     = "<!--"             

data2         = <any string that doesn't contain a substring that matches not-data2>
not-data2     = script-start / "-->"  

data3         = <any string that doesn't contain a substring that matches not-data3>
not-data3     = script-end / "-->"

script-start  = lt       s c r i p t tag-end
script-end    = lt slash s c r i p t tag-end

lt            =  %x003C ; U+003C LESS-THAN SIGN character (<)
slash         =  %x002F ; U+002F SOLIDUS character (/)

s             =  %x0053 ; U+0053 LATIN CAPITAL LETTER S
s             =/ %x0073 ; U+0073 LATIN SMALL LETTER S
c             =  %x0043 ; U+0043 LATIN CAPITAL LETTER C
c             =/ %x0063 ; U+0063 LATIN SMALL LETTER C
r             =  %x0052 ; U+0052 LATIN CAPITAL LETTER R
r             =/ %x0072 ; U+0072 LATIN SMALL LETTER R
i             =  %x0049 ; U+0049 LATIN CAPITAL LETTER I
i             =/ %x0069 ; U+0069 LATIN SMALL LETTER I
p             =  %x0050 ; U+0050 LATIN CAPITAL LETTER P
p             =/ %x0070 ; U+0070 LATIN SMALL LETTER P
t             =  %x0054 ; U+0054 LATIN CAPITAL LETTER T
t             =/ %x0074 ; U+0074 LATIN SMALL LETTER T

tag-end       =  %x0009 ; U+0009 CHARACTER TABULATION (tab)
tag-end       =/ %x000A ; U+000A LINE FEED (LF)
tag-end       =/ %x000C ; U+000C FORM FEED (FF)
tag-end       =/ %x0020 ; U+0020 SPACE
tag-end       =/ %x002F ; U+002F SOLIDUS (/)
tag-end       =/ %x003E ; U+003E GREATER-THAN SIGN (>)

When a script element contains script documentation, there are further restrictions on the contents of the element, as described in the section below.

4.3.1.3 Inline documentation for external scripts

If a script element's src attribute is specified, then the contents of the script element, if any, must be such that the value of the text IDL attribute, which is derived from the element's contents, matches the documentation production in the following ABNF, the character set for which is Unicode. [ABNF]

documentation = *( *( space / tab / comment ) [ line-comment ] newline )
comment       = slash star *( not-star / star not-slash ) 1*star slash
line-comment  = slash slash *not-newline

; characters
tab           = %x0009 ; U+0009 CHARACTER TABULATION (tab)
newline       = %x000A ; U+000A LINE FEED (LF)
space         = %x0020 ; U+0020 SPACE
star          = %x002A ; U+002A ASTERISK (*)
slash         = %x002F ; U+002F SOLIDUS (/)
not-newline   = %x0000-0009 / %x000B-10FFFF
                ; a Unicode character other than U+000A LINE FEED (LF)
not-star      = %x0000-0029 / %x002B-10FFFF
                ; a Unicode character other than U+002A ASTERISK (*)
not-slash     = %x0000-002E / %x0030-10FFFF
                ; a Unicode character other than U+002F SOLIDUS (/)

This corresponds to putting the contents of the element in JavaScript comments.

This requirement is in addition to the earlier restrictions on the syntax of contents of script elements.

This allows authors to include documentation, such as license information or API information, inside their documents while still referring to external script files. The syntax is constrained so that authors don't accidentally include what looks like valid script while also providing a src attribute.

<script src="cool-effects.js">
 // create new instances using:
 //    var e = new Effect();
 // start the effect using .play, stop using .stop:
 //    e.play();
 //    e.stop();
</script>

4.3.1.4 Interaction of `script` elements and XSLT

This section is non-normative.

This specification does not define how XSLT interacts with the script element (or, indeed, how XSLT processing triggers the stop parsing steps, how it interacts with the navigation algorithm, or how it fits in with the event loop). However, in the absence of another specification actually defining this, here are some guidelines for implementors, based on existing implementations:

When an XSLT transformation program is triggered by an <?xml-stylesheet?> processing instruction and the browser implements a direct-to-DOM transformation, script elements created by the XSLT processor need to be marked "parser-inserted" and run in document order (modulo scripts marked defer or async), asynchronously while the transformation is occurring.
The XSLTProcessor.transformToDocument() method adds elements to a Document that is not in a browsing context, and, accordingly, any script elements they create need to have their "already started" flag set in the prepare a script algorithm and never get executed (scripting is disabled). Such script elements still need to be marked "parser-inserted", though, such that their async IDL attribute will return false in the absence of an async content attribute.
The XSLTProcessor.transformToFragment() method needs to create a fragment that is equivalent to one built manually by creating the elements using document.createElementNS(). For instance, it needs to create script elements that aren't "parser-inserted" and that don't have their "already started" flag set, so that they will execute when the fragment is inserted into a document.

The main distinction between the first two cases and the last case is that the first two operate on Documents and the last operates on a fragment.

4.3.2 The `noscript` element

Categories: Metadata content.; Flow content.; Phrasing content.
Contexts in which this element can be used:: In a head element of an HTML document, if there are no ancestor noscript elements.; Where phrasing content is expected in HTML documents, if there are no ancestor noscript elements.
Content model:: When scripting is disabled, in a head element: in any order, zero or more link elements, zero or more style elements, and zero or more meta elements.; When scripting is disabled, not in a head element: transparent, but there must be no noscript element descendants.; Otherwise: text that conforms to the requirements given in the prose.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The noscript element represents nothing if scripting is enabled, and represents its children if scripting is disabled. It is used to present different markup to user agents that support scripting and those that don't support scripting, by affecting how the document is parsed.

When used in HTML documents, the allowed content model is as follows:

In a head element, if scripting is disabled for the noscript element

The noscript element must contain only link, style, and meta elements.

In a head element, if scripting is enabled for the noscript element

The noscript element must contain only text, except that invoking the HTML fragment parsing algorithm with the noscript element as the context element and the text contents as the input must result in a list of nodes that consists only of link, style, and meta elements that would be conforming if they were children of the noscript element, and no parse errors.

Outside of head elements, if scripting is disabled for the noscript element

The noscript element's content model is transparent, with the additional restriction that a noscript element must not have a noscript element as an ancestor (that is, noscript can't be nested).

Outside of head elements, if scripting is enabled for the noscript element

The noscript element must contain only text, except that the text must be such that running the following algorithm results in a conforming document with no noscript elements and no script elements, and such that no step in the algorithm causes an HTML parser to flag a parse error:

Remove every script element from the document.
Make a list of every noscript element in the document. For every noscript element in that list, perform the following steps:
1. Let the parent element be the parent element of the noscript element.
2. Take all the children of the parent element that come before the noscript element, and call these elements the before children.
3. Take all the children of the parent element that come after the noscript element, and call these elements the after children.
4. Let s be the concatenation of all the text node children of the noscript element.
5. Set the innerHTML attribute of the parent element to the value of s. (This, as a side-effect, causes the noscript element to be removed from the document.)
6. Insert the before children at the start of the parent element, preserving their original relative order.
7. Insert the after children at the end of the parent element, preserving their original relative order.

All these contortions are required because, for historical reasons, the noscript element is handled differently by the HTML parser based on whether scripting was enabled or not when the parser was invoked.

The noscript element must not be used in XML documents.

The noscript element is only effective in the HTML syntax, it has no effect in the XHTML syntax.

The noscript element has no other requirements. In particular, children of the noscript element are not exempt from form submission, scripting, and so forth, even when scripting is enabled for the element.

In the following example, a noscript element is used to provide fallback for a script.

<form action="calcSquare.php">
 <p>
  <label for=x>Number</label>:
  <input id="x" name="x" type="number">
 </p>
 <script>
  var x = document.getElementById('x');
  var output = document.createElement('p');
  output.textContent = 'Type a number; it will be squared right then!';
  x.form.appendChild(output);
  x.form.onsubmit = function () { return false; }
  x.oninput = function () {
    var v = x.valueAsNumber;
    output.textContent = v + ' squared is ' + v * v;
  };
 </script>
 <noscript>
  <input type=submit value="Calculate Square">
 </noscript>
</form>

When script is disabled, a button appears to do the calculation on the server side. When script is enabled, the value is computed on-the-fly instead.

The noscript element is a blunt instrument. Sometimes, scripts might be enabled, but for some reason the page's script might fail. For this reason, it's generally better to avoid using noscript, and to instead design the script to change the page from being a scriptless page to a scripted page on the fly, as in the next example:

<form action="calcSquare.php">
 <p>
  <label for=x>Number</label>:
  <input id="x" name="x" type="number">
 </p>
 <input id="submit" type=submit value="Calculate Square">
 <script>
  var x = document.getElementById('x');
  var output = document.createElement('p');
  output.textContent = 'Type a number; it will be squared right then!';
  x.form.appendChild(output);
  x.form.onsubmit = function () { return false; }
  x.oninput = function () {
    var v = x.valueAsNumber;
    output.textContent = v + ' squared is ' + v * v;
  };
  var submit = document.getElementById('submit');
  submit.parentNode.removeChild(submit);
 </script>
</form>

The above technique is also useful in XHTML, since noscript is not supported in the XHTML syntax.

4.4 Sections

4.4.1 The `body` element

Categories

Contexts in which this element can be used:

As the second element in an html element.

Content model:

Content attributes:

onafterprint

onbeforeprint

onbeforeunload

onblur

onerror

onfocus

onhashchange

onload

onmessage

onoffline

ononline

onpagehide

onpageshow

onpopstate

onredo

onresize

onscroll

onstorage

onundo

onunload

DOM interface:

interface HTMLBodyElement : HTMLElement {
           attribute Function onafterprint;
           attribute Function onbeforeprint;
           attribute Function onbeforeunload;
           attribute Function onblur;
           attribute Function onerror;
           attribute Function onfocus;
           attribute Function onhashchange;
           attribute Function onload;
           attribute Function onmessage;
           attribute Function onoffline;
           attribute Function ononline;
           attribute Function onpopstate;
           attribute Function onpagehide;
           attribute Function onpageshow;
           attribute Function onredo;
           attribute Function onresize;
           attribute Function onscroll;
           attribute Function onstorage;
           attribute Function onundo;
           attribute Function onunload;
};

The body element represents the main content of the document.

In conforming documents, there is only one body element. The document.body IDL attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

The body element exposes as event handler content attributes a number of the event handlers of the Window object. It also mirrors their event handler IDL attributes.

The onblur, onerror, onfocus, onload, and onscroll event handlers of the Window object, exposed on the body element, shadow the generic event handlers with the same names normally supported by HTML elements.

Thus, for example, a bubbling error event fired on a child of the body element of a Document would first trigger the onerror event handler content attributes of that element, then that of the root html element, and only then would it trigger the onerror event handler content attribute on the body element. This is because the event would bubble from the target, to the body, to the html, to the Document, to the Window, and the event handler on the body is watching the Window not the body. A regular event listener attached to the body using addEventListener(), however, would fire when the event bubbled through the body and not when it reaches the Window object.

This page updates an indicator to show whether or not the user is online:

<!DOCTYPE HTML>
<html>
 <head>
  <title>Online or offline?</title>
  <script>
   function update(online) {
     document.getElementById('status').textContent =
       online ? 'Online' : 'Offline';
   }
  </script>
 </head>
 <body ononline="update(true)"
       onoffline="update(false)"
       onload="update(navigator.onLine)">
  <p>You are: <span id="status">(Unknown)</span></p>
 </body>
</html>

4.4.2 The `section` element

Categories: Flow content.; Sectioning content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The section element represents a generic section of a document or application. A section, in this context, is a thematic grouping of content, typically with a heading.

Examples of sections would be chapters, the various tabbed pages in a tabbed dialog box, or the numbered sections of a thesis. A Web site's home page could be split into sections for an introduction, news items, and contact information.

Authors are encouraged to use the article element instead of the section element when it would make sense to syndicate the contents of the element.

The section element is not a generic container element. When an element is needed for styling purposes or as a convenience for scripting, authors are encouraged to use the div element instead. A general rule is that the section element is appropriate only if the element's contents would be listed explicitly in the document's outline.

In the following example, we see an article (part of a larger Web page) about apples, containing two short sections.

<article>
 <hgroup>
  <h1>Apples</h1>
  <h2>Tasty, delicious fruit!</h2>
 </hgroup>
 <p>The apple is the pomaceous fruit of the apple tree.</p>
 <section>
  <h1>Red Delicious</h1>
  <p>These bright red apples are the most common found in many
  supermarkets.</p>
 </section>
 <section>
  <h1>Granny Smith</h1>
  <p>These juicy, green apples make a great filling for
  apple pies.</p>
 </section>
</article>

Notice how the use of section means that the author can use h1 elements throughout, without having to worry about whether a particular section is at the top level, the second level, the third level, and so on.

Here is a graduation programme with two sections, one for the list of people graduating, and one for the description of the ceremony.

<!DOCTYPE Html>
<Html
 ><Head
   ><Title
     >Graduation Ceremony Summer 2022</Title
   ></Head
 ><Body
   ><H1
     >Graduation</H1
   ><Section
     ><H1
       >Ceremony</H1
     ><P
       >Opening Procession</P
     ><P
       >Speech by Validactorian</P
     ><P
       >Speech by Class President</P
     ><P
       >Presentation of Diplomas</P
     ><P
       >Closing Speech by Headmaster</P
   ></Section
   ><Section
     ><H1
       >Graduates</H1
     ><Ul
       ><Li
         >Molly Carpenter</Li
       ><Li
         >Anastasia Luccio</Li
       ><Li
         >Ebenezar McCoy</Li
       ><Li
         >Karrin Murphy</Li
       ><Li
         >Thomas Raith</Li
       ><Li
         >Susan Rodriguez</Li
     ></Ul
   ></Section
 ></Body
></Html>

4.4.3 The `nav` element

Categories: Flow content.; Sectioning content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links.

Not all groups of links on a page need to be in a nav element — the element is primarily intended for sections that consist of major navigation blocks. In particular, it is common for footers to have a short list of links to various pages of a site, such as the terms of service, the home page, and a copyright page. The footer element alone is sufficient for such cases; while a nav element can be used in such cases, it is usually unnecessary.

User agents (such as screen readers) that are targeted at users who can benefit from navigation information being omitted in the initial rendering, or who can benefit from navigation information being immediately available, can use this element as a way to determine what content on the page to initially skip and/or provide on request.

In the following example, the page has several places where links are present, but only one of those places is considered a navigation section.

<body>
 <header>
  <h1>Wake up sheeple!</h1>
  <p><a href="news.html">News</a> -
     <a href="blog.html">Blog</a> -
     <a href="forums.html">Forums</a></p>
  <p>Last Modified: <time>2009-04-01</time></p>
  <nav>
   <h1>Navigation</h1>
   <ul>
    <li><a href="articles.html">Index of all articles</a></li>
    <li><a href="today.html">Things sheeple need to wake up for today</a></li>
    <li><a href="successes.html">Sheeple we have managed to wake</a></li>
   </ul>
  </nav>
 </header>
 <div>
  <article>
   <header>
    <h1>My Day at the Beach</h1>
   </header>
   <div>
    <p>Today I went to the beach and had a lot of fun.</p>
    ...more content...
   </div>
   <footer>
    <p>Posted <time pubdate="" datetime="2009-10-10T14:36-08:00">Thursday</time>.</p>
   </footer>
  </article>
  ...more blog posts...
 </div>
 <footer>
  <p>Copyright © 2006 The Example Company</p>
  <p><a href="about.html">About</a> -
     <a href="policy.html">Privacy Policy</a> -
     <a href="contact.html">Contact Us</a></p>
 </footer>
</body>

Notice the div elements being used to wrap all the contents of the page other than the header and footer, and all the contents of the blog entry other than its header and footer.

In the following example, there are two nav elements, one for primary navigation around the site, and one for secondary navigation around the page itself.

<body>
 <h1>The Wiki Center Of Exampland</h1>
 <nav>
  <ul>
   <li><a href="/">Home</a></li>
   <li><a href="/events">Current Events</a></li>
   ...more...
  </ul>
 </nav>
 <article>
  <header>
   <h1>Demos in Exampland</h1>
   <p>Written by A. N. Other.</p>
  </header>
  <nav>
   <ul>
    <li><a href="#public">Public demonstrations</a></li>
    <li><a href="#destroy">Demolitions</a></li>
    ...more...
   </ul>
  </nav>
  <div>
   <section id="public">
    <h1>Public demonstrations</h1>
    <p>...more...</p>
   </section>
   <section id="destroy">
    <h1>Demolitions</h1>
    <p>...more...</p>
   </section>
   ...more...
  </div>
  <footer>
   <p><a href="?edit">Edit</a> | <a href="?delete">Delete</a> | <a href="?Rename">Rename</a></p>
  </footer>
 </article>
 <footer>
  <p><small>© copyright 1998 Exampland Emperor</small></p>
 </footer>
</body>

A nav element doesn't have to contain a list, it can contain other kinds of content as well. In this navigation block, links are provided in prose:

<nav>
 <h1>Navigation</h1>
 <p>You are on my home page. To the north lies <a href="/blog">my
 blog</a>, from whence the sounds of battle can be heard. To the east
 you can see a large mountain, upon which many <a
 href="/school">school papers</a> are littered. Far up thus mountain
 you can spy a little figure who appears to be me, desperately
 scribbling a <a href="/school/thesis">thesis</a>.</p>
 <p>To the west are several exits. One fun-looking exit is labeled <a
 href="http://games.example.com/">"games"</a>. Another more
 boring-looking exit is labeled <a
 href="http://isp.example.net/">ISP™</a>.</p>
 <p>To the south lies a dark and dank <a href="/about">contacts
 page</a>. Cobwebs cover its disused entrance, and at one point you
 see a rat run quickly out of the page.</p>
</nav>

4.4.4 The `article` element

Categories: Flow content.; Sectioning content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The article element represents a self-contained composition in a document, page, application, or site and that is, in principle, independently distributable or reusable, e.g. in syndication. This could be a forum post, a magazine or newspaper article, a blog entry, a user-submitted comment, an interactive widget or gadget, or any other independent item of content.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a blog entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the blog entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

When used specifically with content to be redistributed in syndication, the article element is similar in purpose to the entry element in Atom. [ATOM]

The time element's pubdate attribute can be used to provide the publication date for an article element.

This example shows a blog post using the article element:

<article>
 <header>
  <h1>The Very First Rule of Life</h1>
  <p><time pubdate datetime="2009-10-09T14:28-08:00"></time></p>
 </header>
 <p>If there's a microphone anywhere near you, assume it's hot and
 sending whatever you're saying to the world. Seriously.</p>
 <p>...</p>
 <footer>
  <a href="?comments=1">Show comments...</a>
 </footer>
</article>

Here is that same blog post, but showing some of the comments:

<article>
 <header>
  <h1>The Very First Rule of Life</h1>
  <p><time pubdate datetime="2009-10-09T14:28-08:00"></time></p>
 </header>
 <p>If there's a microphone anywhere near you, assume it's hot and
 sending whatever you're saying to the world. Seriously.</p>
 <p>...</p>
 <section>
  <h1>Comments</h1>
  <article>
   <footer>
    <p>Posted by: George Washington</p>
    <p><time pubdate datetime="2009-10-10T19:10-08:00"></time></p>
   </footer>
   <p>Yeah! Especially when talking about your lobbyist friends!</p>
  </article>
  <article>
   <footer>
    <p>Posted by: George Hammond</p>
    <p><time pubdate datetime="2009-10-10T19:15-08:00"></time></p>
   </footer>
   <p>Hey, you have the same first name as me.</p>
  </article>
 </section>
</article>

Notice the use of footer to give the information for each comment (such as who wrote it and when): the footer element can appear at the start of its section when appropriate, such as in this case. (Using header in this case wouldn't be wrong either; it's mostly a matter of authoring preference.)

4.4.5 The `aside` element

Categories: Flow content.; Sectioning content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

The element can be used for typographical effects like pull quotes or sidebars, for advertising, for groups of nav elements, and for other content that is considered separate from the main content of the page.

It's not appropriate to use the aside element just for parentheticals, since those are part of the main flow of the document.

The following example shows how an aside is used to mark up background material on Switzerland in a much longer news story on Europe.

<aside>
 <h1>Switzerland</h1>
 <p>Switzerland, a land-locked country in the middle of geographic
 Europe, has not joined the geopolitical European Union, though it is
 a signatory to a number of European treaties.</p>
</aside>

The following example shows how an aside is used to mark up a pull quote in a longer article.

...

<p>He later joined a large company, continuing on the same work.
<q>I love my job. People ask me what I do for fun when I'm not at
work. But I'm paid to do my hobby, so I never know what to
answer. Some people wonder what they would do if they didn't have to
work... but I know what I would do, because I was unemployed for a
year, and I filled that time doing exactly what I do now.</q></p>

<aside>
 <q> People ask me what I do for fun when I'm not at work. But I'm
 paid to do my hobby, so I never know what to answer. </q>
</aside>

<p>Of course his work — or should that be hobby? —
isn't his only passion. He also enjoys other pleasures.</p>

...

The following extract shows how aside can be used for blogrolls and other side content on a blog:

<body>
 <header>
  <h1>My wonderful blog</h1>
  <p>My tagline</p>
 </header>
 <aside>
  <!-- this aside contains two sections that are tangentially related
  to the page, namely, links to other blogs, and links to blog posts
  from this blog -->
  <nav>
   <h1>My blogroll</h1>
   <ul>
    <li><a href="http://blog.example.com/">Example Blog</a>
   </ul>
  </nav>
  <nav>
   <h1>Archives</h1>
   <ol reversed>
    <li><a href="/last-post">My last post</a>
    <li><a href="/first-post">My first post</a>
   </ol>
  </nav>
 </aside>
 <aside>
  <!-- this aside is tangentially related to the page also, it
  contains twitter messages from the blog author -->
  <h1>Twitter Feed</h1>
  <blockquote cite="http://twitter.example.net/t31351234">
   I'm on vacation, writing my blog.
  </blockquote>
  <blockquote cite="http://twitter.example.net/t31219752">
   I'm going to go on vacation soon.
  </blockquote>
 </aside>
 <article>
  <!-- this is a blog post -->
  <h1>My last post</h1>
  <p>This is my last post.</p>
  <footer>
   <p><a href="/last-post" rel=bookmark>Permalink</a>
  </footer>
 </article>
 <article>
  <!-- this is also a blog post -->
  <h1>My first post</h1>
  <p>This is my first post.</p>
  <aside>
   <!-- this aside is about the blog post, since it's inside the
   <article> element; it would be wrong, for instance, to put the
   blogroll here, since the blogroll isn't really related to this post
   specifically, only to the page as a whole -->
   <h1>Posting</h1>
   <p>While I'm thinking about it, I wanted to say something about
   posting. Posting is fun!</p>
  </aside>
  <footer>
   <p><a href="/first-post" rel=bookmark>Permalink</a>
  </footer>
 </article>
 <footer>
  <nav>
   <a href="/archives">Archives</a> —
   <a href="/about">About me</a> —
   <a href="/copyright">Copyright</a>
  </nav>
 </footer>
</body>

4.4.6 The `h1`, `h2`, `h3`, `h4`, `h5`, and `h6` elements

Categories

Heading content.

Contexts in which this element can be used:

As a child of an hgroup element.

Where flow content is expected.

Content model:

Content attributes:

DOM interface:

interface HTMLHeadingElement : HTMLElement {};

These elements represent headings for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

These two snippets are equivalent:

<body>
<h1>Let's call it a draw(ing surface)</h1>
<h2>Diving in</h2>
<h2>Simple shapes</h2>
<h2>Canvas coordinates</h2>
<h3>Canvas coordinates diagram</h3>
<h2>Paths</h2>
</body>

<body>
 <h1>Let's call it a draw(ing surface)</h1>
 <section>
  <h1>Diving in</h1>
 </section>
 <section>
  <h1>Simple shapes</h1>
 </section>
 <section>
  <h1>Canvas coordinates</h1>
  <section>
   <h1>Canvas coordinates diagram</h1>
  </section>
 </section>
 <section>
  <h1>Paths</h1>
 </section>
</body>

4.4.7 The `hgroup` element

Categories: Flow content.; Heading content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: One or more h1, h2, h3, h4, h5, and/or h6 elements.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The hgroup element represents the heading of a section. The element is used to group a set of h1–h6 elements when the heading has multiple levels, such as subheadings, alternative titles, or taglines.

For the purposes of document summaries, outlines, and the like, the text of hgroup elements is defined to be the text of the highest ranked h1–h6 element descendant of the hgroup element, if there are any such elements, and the first such element if there are multiple elements with that rank. If there are no such elements, then the text of the hgroup element is the empty string.

Other elements of heading content in the hgroup element indicate subheadings or subtitles.

The rank of an hgroup element is the rank of the highest-ranked h1–h6 element descendant of the hgroup element, if there are any such elements, or otherwise the same as for an h1 element (the highest rank).

The section on headings and sections defines how hgroup elements are assigned to individual sections.

Here are some examples of valid headings. In each case, the emphasized text represents the text that would be used as the heading in an application extracting heading data and ignoring subheadings.

<hgroup>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</hgroup>

<hgroup>
 <h1>Dr. Strangelove</h1>
 <h2>Or: How I Learned to Stop Worrying and Love the Bomb</h2>
</hgroup>

The point of using hgroup in these examples is to mask the h2 element (which acts as a secondary title) from the outline algorithm.

4.4.8 The `header` element

Categories: Flow content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content, but with no header or footer element descendants.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The header element represents a group of introductory or navigational aids.

A header element is intended to usually contain the section's heading (an h1–h6 element or an hgroup element), but this is not required. The header element can also be used to wrap a section's table of contents, a search form, or any relevant logos.

Here are some sample headers. This first one is for a game:

<header>
 <p>Welcome to...</p>
 <h1>Voidwars!</h1>
</header>

The following snippet shows how the element can be used to mark up a specification's header:

<header>
 <hgroup>
  <h1>Scalable Vector Graphics (SVG) 1.2</h1>
  <h2>W3C Working Draft 27 October 2004</h2>
 </hgroup>
 <dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/">http://www.w3.org/TR/2004/WD-SVG12-20041027/</a></dd>
  <dt>Previous version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/">http://www.w3.org/TR/2004/WD-SVG12-20040510/</a></dd>
  <dt>Latest version of SVG 1.2:</dt>
  <dd><a href="http://www.w3.org/TR/SVG12/">http://www.w3.org/TR/SVG12/</a></dd>
  <dt>Latest SVG Recommendation:</dt>
  <dd><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></dd>
  <dt>Editor:</dt>
  <dd>Dean Jackson, W3C, <a href="mailto:dean@w3.org">dean@w3.org</a></dd>
  <dt>Authors:</dt>
  <dd>See <a href="#authors">Author List</a></dd>
 </dl>
 <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notic ...
</header>

The header element is not sectioning content; it doesn't introduce a new section.

In this example, the page has a page heading given by the h1 element, and two subsections whose headings are given by h2 elements. The content after the header element is still part of the last subsection started in the header element, because the header element doesn't take part in the outline algorithm.

<body>
 <header>
  <h1>Little Green Guys With Guns</h1>
  <nav>
   <ul>
    <li><a href="/games">Games</a>
    <li><a href="/forum">Forum</a>
    <li><a href="/download">Download</a>
   </ul>
  </nav>
  <h2>Important News</h2> <!-- this starts a second subsection -->
  <!-- this is part of the subsection entitled "Important News" -->
  <p>To play today's games you will need to update your client.</p>
  <h2>Games</h2> <!-- this starts a third subsection -->
 </header>
 <p>You have three active games:</p>
 <!-- this is still part of the subsection entitled "Games" -->
 ...

Categories: Flow content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content, but with no header or footer element descendants.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The footer element represents a footer for its nearest ancestor sectioning content or sectioning root element. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

When the footer element contains entire sections, they represent appendices, indexes, long colophons, verbose license agreements, and other such content.

Contact information for the author or editor of a section belongs in an address element, possibly itself inside a footer.

Footers don't necessarily have to appear at the end of a section, though they usually do.

When the nearest ancestor sectioning content or sectioning root element is the body element, then it applies to the whole page.

The footer element is not sectioning content; it doesn't introduce a new section.

Here is a page with two footers, one at the top and one at the bottom, with the same content:

<body>
 <footer><a href="../">Back to index...</a></footer>
 <hgroup>
  <h1>Lorem ipsum</h1>
  <h2>The ipsum of all lorems</h2>
 </hgroup>
 <p>A dolor sit amet, consectetur adipisicing elit, sed do eiusmod
 tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
 veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
 ea commodo consequat. Duis aute irure dolor in reprehenderit in
 voluptate velit esse cillum dolore eu fugiat nulla
 pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
 culpa qui officia deserunt mollit anim id est laborum.</p>
 <footer><a href="../">Back to index...</a></footer>
</body>

Here is an example which shows the footer element being used both for a site-wide footer and for a section footer.

<!DOCTYPE HTML>
<HTML><HEAD>
<TITLE>The Ramblings of a Scientist</TITLE>
<BODY>
<H1>The Ramblings of a Scientist</H1>
<ARTICLE>
 <H1>Episode 15</H1>
 <VIDEO SRC="/fm/015.ogv" CONTROLS PRELOAD>
  <P><A HREF="/fm/015.ogv">Download video</A>.</P>
 </VIDEO>
 <FOOTER> <!-- footer for article -->
  <P>Published <TIME PUBDATE DATETIME="2009-10-21T18:26-07:00"></TIME></P>
 </FOOTER>
</ARTICLE>
<ARTICLE>
 <H1>My Favorite Trains</H1>
 <P>I love my trains. My favorite train of all time is a Köf.</P>
 <P>It is fun to see them pull some coal cars because they look so
 dwarfed in comparison.</P>
 <FOOTER> <!-- footer for article -->
  <P>Published <TIME PUBDATE DATETIME="2009-09-15T14:54-07:00"></TIME></P>
 </FOOTER>
</ARTICLE>
<FOOTER> <!-- site wide footer -->
 <NAV>
  <P><A HREF="/credits.html">Credits</A> —
     <A HREF="/tos.html">Terms of Service</A> —
     <A HREF="/index.html">Blog Index</A></P>
 </NAV>
 <P>Copyright © 2009 Gordon Freeman</P>
</FOOTER>
</BODY>
</HTML>

Some site designs have what is sometimes referred to as "fat footers" — footers that contain a lot of material, including images, links to other articles, links to pages for sending feedback, special offers... in some ways, a whole "front page" in the footer.

This fragment shows the bottom of a page on a site with a "fat footer":

...
 <footer>
  <nav>
   <section>
    <h1>Articles</h1>
    <p><img src="http://dev.w3.org/html5/spec/images/somersaults.jpeg" alt=""> Go to the gym with
    our somersaults class! Our teacher Jim takes you through the paces
    in this two-part article. <a href="articles/somersaults/1">Part
    1</a> · <a href="articles/somersaults/1">Part 2</a></p>
    <p><img src="http://dev.w3.org/html5/spec/images/kindplus.jpeg"> Tired of walking on the edge of
    a clif<!-- sic -->? Our guest writer Lara shows you how to bumble
    your way through the bars. <a href="articles/kindplus/1">Read
    more...</a></p>
    <p><img src="http://dev.w3.org/html5/spec/images/crisps.jpeg"> The chips are down, now all
    that's left is a potato. What can you do with it? <a
    href="articles/crisps/1">Read more...</a></p>
   </section>
   <ul>
    <li> <a href="/about">About us...</a>
    <li> <a href="/feedback">Send feedback!</a>
    <li> <a href="/sitemap">Sitemap</a>
   </ul>
  </nav>
  <p><small>Copyright © 2015 The Snacker —
  <a href="/tos">Terms of Service</a></small></p>
 </footer>
</body>

4.4.10 The `address` element

Categories: Flow content.; formatBlock candidate.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Flow content, but with no heading content descendants, no sectioning content descendants, and no header, footer, or address element descendants.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The address element represents the contact information for its nearest article or body element ancestor. If that is the body element, then the contact information applies to the document as a whole.

For example, a page at the W3C Web site related to HTML might include the following contact information:

<ADDRESS>
 <A href="../People/Raggett/">Dave Raggett</A>,
 <A href="../People/Arnaud/">Arnaud Le Hors</A>,
 contact persons for the <A href="Activity">W3C HTML Activity</A>
</ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are in fact the relevant contact information. (The p element is the appropriate element for marking up postal addresses in general.)

The address element must not contain information other than contact information.

For example, the following is non-conforming use of the address element:

<ADDRESS>Last Modified: 1999/12/24 23:37:50</ADDRESS>

Typically, the address element would be included along with other information in a footer element.

The contact information for a node node is a collection of address elements defined by the first applicable entry from the following list:

If node is an article element
If node is a body element: The contact information consists of all the address elements that have node as an ancestor and do not have another body or article element ancestor that is a descendant of node.
If node has an ancestor element that is an article element
If node has an ancestor element that is a body element: The contact information of node is the same as the contact information of the nearest article or body element ancestor, whichever is nearest.
If node's Document has a body element: The contact information of node is the same as the contact information of the body element of the Document.
Otherwise: There is no contact information for node.

User agents may expose the contact information of a node to the user, or use it for other purposes, such as indexing sections based on the sections' contact information.

In this example the footer contains contact information and a copyright notice.

<footer>
 <address>
  For more details, contact
  <a href="mailto:js@example.com">John Smith</a>.
 </address>
 <p><small>© copyright 2038 Example Corp.</small></p>
</footer>

4.4.11 Headings and sections

The h1–h6 elements and the hgroup element are headings.

The first element of heading content in an element of sectioning content represents the heading for that section. Subsequent headings of equal or higher rank start new (implied) sections, headings of lower rank start implied subsections that are part of the previous one. In both cases, the element represents the heading of the implied section.

Certain elements are said to be sectioning roots, including blockquote and td elements. These elements can have their own outlines, but the sections and headings inside these elements do not contribute to the outlines of their ancestors.

Sectioning content elements are always considered subsections of their nearest ancestor sectioning root or their nearest ancestor element of sectioning content, whichever is nearest, regardless of what implied sections other headings may have created.

For the following fragment:

<body>
 <h1>Foo</h1>
 <h2>Bar</h2>
 <blockquote>
  <h3>Bla</h3>
 </blockquote>
 <p>Baz</p>
 <h2>Quux</h2>
 <section>
  <h3>Thud</h3>
 </section>
 <p>Grunt</p>
</body>

...the structure would be:

Foo (heading of explicit body section, containing the "Grunt" paragraph)
1. Bar (heading starting implied section, containing a block quote and the "Baz" paragraph)
2. Quux (heading starting implied section with no content other than the heading itself)
3. Thud (heading of explicit section section)

Notice how the section ends the earlier implicit section so that a later paragraph ("Grunt") is back at the top level.

Sections may contain headings of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explicitly wrap sections in elements of sectioning content, instead of relying on the implicit sections generated by having multiple headings in one element of sectioning content.

For example, the following is correct:

<body>
 <h4>Apples</h4>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <h6>Sweet</h6>
  <p>Red apples are sweeter than green ones.</p>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

However, the same document would be more clearly expressed as:

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <section>
   <h3>Sweet</h3>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h2>Color</h2>
  <p>Apples come in various colors.</p>
 </section>
</body>

Both of the documents above are semantically identical and would produce the same outline in compliant user agents.

This third example is also semantically identical, and might be easier to maintain (e.g. if sections are often moved around in editing):

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h1>Taste</h1>
  <p>They taste lovely.</p>
  <section>
   <h1>Sweet</h1>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

4.4.11.1 Creating an outline

This section defines an algorithm for creating an outline for a sectioning content element or a sectioning root element. It is defined in terms of a walk over the nodes of a DOM tree, in tree order, with each node being visited when it is entered and when it is exited during the walk.

The outline for a sectioning content element or a sectioning root element consists of a list of one or more potentially nested sections. A section is a container that corresponds to some nodes in the original DOM tree. Each section can have one heading associated with it, and can contain any number of further nested sections. The algorithm for the outline also associates each node in the DOM tree with a particular section and potentially a heading. (The sections in the outline aren't section elements, though some may correspond to such elements — they are merely conceptual sections.)

The following markup fragment:

<body>
 <h1>A</h1>
 <p>B</p>
 <h2>C</h2>
 <p>D</p>
 <h2>E</h2>
 <p>F</p>
</body>

...results in the following outline being created for the body node (and thus the entire document):

Section created for body node.

Associated with heading "A".

Also associated with paragraph "B".

Nested sections:
1. Section implied for first h2 element.
  
  Associated with heading "C".
  
  Also associated with paragraph "D".
  
  No nested sections.
2. Section implied for second h2 element.
  
  Associated with heading "E".
  
  Also associated with paragraph "F".
  
  No nested sections.

The algorithm that must be followed during a walk of a DOM subtree rooted at a sectioning content element or a sectioning root element to determine that element's outline is as follows:

Let current outlinee be null. (It holds the element whose outline is being created.)
Let current section be null. (It holds a pointer to a section, so that elements in the DOM can all be associated with a section.)
Create a stack to hold elements, which is used to handle nesting. Initialize this stack to empty.
As you walk over the DOM in tree order, trigger the first relevant step below for each element as you enter and exit it.
If you are exiting an element and that element is the element at the top of the stack

The element being exited is a heading content element.

Pop that element from the stack.

If the top of the stack is a heading content element

Do nothing.

When entering a sectioning content element or a sectioning root element

If current outlinee is not null, and the current section has no heading, create an implied heading and let that be the heading for the current section.

If current outlinee is not null, push current outlinee onto the stack.

Let current outlinee be the element that is being entered.

Let current section be a newly created section for the current outlinee element.

Associate current outlinee with current section.

Let there be a new outline for the new current outlinee, initialized with just the new current section as the only section in the outline.

When exiting a sectioning content element, if the stack is not empty

Pop the top element from the stack, and let the current outlinee be that element.

Let current section be the last section in the outline of the current outlinee element.

Append the outline of the sectioning content element being exited to the current section. (This does not change which section is the last section in the outline.)

When exiting a sectioning root element, if the stack is not empty
Run these steps:
1. Pop the top element from the stack, and let the current outlinee be that element.
2. Let current section be the last section in the outline of the current outlinee element.
3. Finding the deepest child: If current section has no child sections, stop these steps.
4. Let current section be the last child section of the current current section.
5. Go back to the substep labeled finding the deepest child.
When exiting a sectioning content element or a sectioning root element

The current outlinee is the element being exited.

Let current section be the first section in the outline of the current outlinee element.

Skip to the next step in the overall set of steps. (The walk is over.)

If the current outlinee is null

Do nothing.

When entering a heading content element
If the current section has no heading, let the element being entered be the heading for the current section.

Otherwise, if the element being entered has a rank equal to or greater than the heading of the last section of the outline of the current outlinee, then create a new section and append it to the outline of the current outlinee element, so that this new section is the new last section of that outline. Let current section be that new section. Let the element being entered be the new heading for the current section.

Otherwise, run these substeps:
1. Let candidate section be current section.
2. If the element being entered has a rank lower than the rank of the heading of the candidate section, then create a new section, and append it to candidate section. (This does not change which section is the last section in the outline.) Let current section be this new section. Let the element being entered be the new heading for the current section. Abort these substeps.
3. Let new candidate section be the section that contains candidate section in the outline of current outlinee.
4. Let candidate section be new candidate section.
5. Return to step 2.
Push the element being entered onto the stack. (This causes the algorithm to skip any descendants of the element.)

Recall that h1 has the highest rank, and h6 has the lowest rank.
Otherwise

Do nothing.
In addition, whenever you exit a node, after doing the steps above, if the node is not associated with a section yet and current section is not null, associate the node with the section current section.
If the current outlinee is null, then there was no sectioning content element or sectioning root element in the DOM. There is no outline. Abort these steps.
Associate any nodes that were not associated with a section in the steps above with current outlinee as their section.
Associate all nodes with the heading of the section with which they are associated, if any.
If current outlinee is the body element, then the outline created for that element is the outline of the entire document.

The tree of sections created by the algorithm above, or a proper subset thereof, must be used when generating document outlines, for example when generating tables of contents.

When creating an interactive table of contents, entries should jump the user to the relevant sectioning content element, if the section was created for a real element in the original document, or to the relevant heading content element, if the section in the tree was generated for a heading in the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first heading in the body is to be found.

The outline depth of a heading content element associated with a section section is the number of sections that are ancestors of section in the outline that section finds itself in when the outlines of its Document's elements are created, plus 1. The outline depth of a heading content element not associated with a section is 1.

User agents should provide default headings for sections that do not have explicit section headings.

Consider the following snippet:

<body>
 <nav>
  <p><a href="/">Home</a></p>
 </nav>
 <p>Hello world.</p>
 <aside>
  <p>My cat is cute.</p>
 </aside>
</body>

Although it contains no headings, this snippet has three sections: a document (the body) with two subsections (a nav and an aside). A user agent could present the outline as follows:

Untitled document
1. Navigation
2. Sidebar

These default headings ("Untitled document", "Navigation", "Sidebar") are not specified by this specification, and might vary with the user's language, the page's language, the user's preferences, the user agent implementor's preferences, etc.

The following JavaScript function shows how the tree walk could be implemented. The root argument is the root of the tree to walk, and the enter and exit arguments are callbacks that are called with the nodes as they are entered and exited. [ECMA262]

function (root, enter, exit) {
  var node = root;
  start: while (node) {
    enter(node);
    if (node.firstChild) {
      node = node.firstChild;
      continue start;
    }
    while (node) {
      exit(node);
      if (node.nextSibling) {
        node = node.nextSibling;
        continue start;
      }
      if (node == root)
        node = null;
      else
        node = node.parentNode;
    }
  }
}

4.5 Grouping content

4.5.1 The `p` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Content attributes:

DOM interface:

interface HTMLParagraphElement : HTMLElement {};

The p element represents a paragraph.

While paragraphs are usually represented in visual media by blocks of text that are physically separated from adjacent blocks through blank lines, a style sheet or user agent would be equally justified in presenting paragraph breaks in a different manner, for instance using inline pilcrows (¶).

The following examples are conforming HTML fragments:

<p>The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.</p>

<fieldset>
 <legend>Personal information</legend>
 <p>
   <label>Name: <input name="n"></label>
   <label><input name="anon" type="checkbox"> Hide from other users</label>
 </p>
 <p><label>Address: <textarea name="a"></textarea></label></p>
</fieldset>

<p>There was once an example from Femley,<br>
Whose markup was of dubious quality.<br>
The validator complained,<br>
So the author was pained,<br>
To move the error from the markup to the rhyming.</p>

The p element should not be used when a more specific element is more appropriate.

The following example is technically correct:

<section>
 <!-- ... -->
 <p>Last modified: 2001-04-23</p>
 <p>Author: fred@example.com</p>
</section>

However, it would be better marked-up as:

<section>
 <!-- ... -->
 <footer>Last modified: 2001-04-23</footer>
 <address>Author: fred@example.com</address>
</section>

Or:

<section>
 <!-- ... -->
 <footer>
  <p>Last modified: 2001-04-23</p>
  <address>Author: fred@example.com</address>
 </footer>
</section>

4.5.2 The `hr` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Empty.

Content attributes:

DOM interface:

interface HTMLHRElement : HTMLElement {};

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

The following fictional extract from a project manual shows two sections that use the hr element to separate topics within the section.

<section>
 <h1>Communication</h1>
 <p>There are various methods of communication. This section
 covers a few of the important ones used by the project.</p>
 <hr>
 <p>Communication stones seem to come in pairs and have mysterious
 properties:</p>
 <ul>
  <li>They can transfer thoughts in two directions once activated
  if used alone.</li>
  <li>If used with another device, they can transfer one's
  consciousness to another body.</li>
  <li>If both stones are used with another device, the
  consciousnesses switch bodies.</li>
 </ul>
 <hr>
 <p>Radios use the electromagnetic spectrum in the meter range and
 longer.</p>
 <hr>
 <p>Signal flares use the electromagnetic spectrum in the
 nanometer range.</p>
</section>
<section>
 <h1>Food</h1>
 <p>All food at the project is rationed:</p>
 <dl>
  <dt>Potatoes</dt>
  <dd>Two per day</dd>
  <dt>Soup</dt>
  <dd>One bowl per day</dd>
 </dl>
 <hr>
 <p>Cooking is done by the chefs on a set rotation.</p>
</section>

There is no need for an hr element between the sections themselves, since the section elements and the h1 elements imply thematic changes themselves.

The following extract from Pandora's Star by Peter F. Hamilton shows two paragraphs that precede a scene change and the paragraph that follows it. The scene change, represented in the printed book by a gap containing a solitary centered star between the second and third paragraphs, is here represented using the hr element.

<p>Dudley was ninety-two, in his second life, and fast approaching
time for another rejuvenation. Despite his body having the physical
age of a standard fifty-year-old, the prospect of a long degrading
campaign within academia was one he regarded with dread. For a
supposedly advanced civilization, the Intersolar Commonwearth could be
appallingly backward at times, not to mention cruel.</p>
<p><i>Maybe it won't be that bad</i>, he told himself. The lie was
comforting enough to get him through the rest of the night's
shift.</p>
<hr>
<p>The Carlton AllLander drove Dudley home just after dawn. Like the
astronomer, the vehicle was old and worn, but perfectly capable of
doing its job. It had a cheap diesel engine, common enough on a
semi-frontier world like Gralmond, although its drive array was a
thoroughly modern photoneural processor. With its high suspension and
deep-tread tyres it could plough along the dirt track to the
observatory in all weather and seasons, including the metre-deep snow
of Gralmond's winters.</p>

The hr element does not affect the document's outline.

4.5.3 The `pre` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Content attributes:

DOM interface:

interface HTMLPreElement : HTMLElement {};

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

In the HTML syntax, a leading newline character immediately following the pre element start tag is stripped.

Some examples of cases where the pre element could be used:

Including an e-mail, with paragraphs indicated by blank lines, lists indicated by lines prefixed with a bullet, and so on.
Including fragments of computer code, with structure indicated according to the conventions of that language.
Displaying ASCII art.

Authors are encouraged to consider how preformatted text will be experienced when the formatting is lost, as will be the case for users of speech synthesizers, braille displays, and the like. For cases like ASCII art, it is likely that an alternative presentation, such as a textual description, would be more universally accessible to the readers of the document.

To represent a block of computer code, the pre element can be used with a code element; to represent a block of computer output the pre element can be used with a samp element. Similarly, the kbd element can be used within a pre element to indicate text that the user is to enter.

A newline in a pre element should separate paragraphs for the purposes of the Unicode bidirectional algorithm. This requirement may be implemented indirectly through the style layer. For example, an HTML+CSS user agent could implement these requirements by implementing the CSS 'unicode-bidi' property. [BIDI] [CSS]

In the following snippet, a sample of computer code is presented.

<p>This is the <code>Panel</code> constructor:</p>
<pre><code>function Panel(element, canClose, closeHandler) {
  this.element = element;
  this.canClose = canClose;
  this.closeHandler = function () { if (closeHandler) closeHandler() };
}</code></pre>

In the following snippet, samp and kbd elements are mixed in the contents of a pre element to show a session of Zork I.

<pre><samp>You are in an open field west of a big white house with a boarded
front door.
There is a small mailbox here.

></samp> <kbd>open mailbox</kbd>

<samp>Opening the mailbox reveals:
A leaflet.

></samp></pre>

The following shows a contemporary poem that uses the pre element to preserve its unusual formatting, which forms an intrinsic part of the poem itself.

<pre>                maxling

it is with a          heart
               heavy

that i admit loss of a feline
        so           loved

a friend lost to the
        unknown
                                (night)

~cdr 11dec07</pre>

4.5.4 The `blockquote` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Content attributes:

cite

DOM interface:

interface HTMLQuoteElement : HTMLElement {
           attribute DOMString cite;
};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose address, if it has one, may be cited in the cite attribute.

If the cite attribute is present, it must be a valid URL potentially surrounded by spaces. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The cite IDL attribute must reflect the element's cite content attribute.

This next example shows the use of cite alongside blockquote:

<p>His next piece was the aptly named <cite>Sonnet 130</cite>:</p>
<blockquote cite="http://quotes.example.org/s/sonnet130.html">
  <p>My mistress' eyes are nothing like the sun,<br>
  Coral is far more red, than her lips red,<br>
  ...

This example shows how a forum post could use blockquote to show what post a user is replying to. The article element is used for each post, to mark up the threading.

<article>
 <h1><a href="http://bacon.example.com/?blog=109431">Bacon on a crowbar</a></h1>
 <article>
  <header><strong>t3yw</strong> 12 points 1 hour ago</header>
  <p>I bet a narwhal would love that.</p>
  <footer><a href="?pid=29578">permalink</a></footer>
  <article>
   <header><strong>greg</strong> 8 points 1 hour ago</header>
   <blockquote><p>I bet a narwhal would love that.</p></blockquote>
   <p>Dude narwhals don't eat bacon.</p>
   <footer><a href="?pid=29579">permalink</a></footer>
   <article>
    <header><strong>t3yw</strong> 15 points 1 hour ago</header>
    <blockquote>
     <blockquote><p>I bet a narwhal would love that.</p></blockquote>
     <p>Dude narwhals don't eat bacon.</p>
    </blockquote>
    <p>Next thing you'll be saying they don't get capes and wizard
    hats either!</p>
    <footer><a href="?pid=29580">permalink</a></footer>
    <article>
     <article>
      <header><strong>boing</strong> -5 points 1 hour ago</header>
      <p>narwhals are worse than ceiling cat</p>
      <footer><a href="?pid=29581">permalink</a></footer>
     </article>
    </article>
   </article>
  </article>
  <article>
   <header><strong>fred</strong> 1 points 23 minutes ago</header>
   <blockquote><p>I bet a narwhal would love that.</p></blockquote>
   <p>I bet they'd love to peel a banana too.</p>
   <footer><a href="?pid=29582">permalink</a></footer>
  </article>
 </article>
</article>

This example shows the use of a blockquote for short snippets, demonstrating that one does not have to use p elements inside blockquote elements:

<p>He began his list of "lessons" with the following:</p>
<blockquote>One should never assume that his side of 
the issue will be recognized, let alone that it will 
be conceded to have merits.</blockquote>
<p>He continued with a number of similar points, ending with:</p>
<blockquote>Finally, one should be prepared for the threat 
of breakdown in negotiations at any given moment and not 
be cowed by the possiblity.</blockquote>
<p>We shall now discuss these points...

Examples of how to represent a conversation are shown in a later section; it is not appropriate to use the cite and blockquote elements for this purpose.

4.5.5 The `ol` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Zero or more li elements.

Content attributes:

reversed

start

type

DOM interface:

interface HTMLOListElement : HTMLElement {
           attribute boolean reversed;
           attribute long start;
           attribute DOMString type;
};

The ol element represents a list of items, where the items have been intentionally ordered, such that changing the order would change the meaning of the document.

The items of the list are the li element child nodes of the ol element, in tree order.

The reversed attribute is a boolean attribute. If present, it indicates that the list is a descending list (..., 3, 2, 1). If the attribute is omitted, the list is an ascending list (1, 2, 3, ...).

The start attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1 if the element has no reversed attribute, and is the number of child li elements otherwise.

The first item in the list has the ordinal value given by the ol element's start attribute, unless that li element has a value attribute with a value that can be successfully parsed, in which case it has the ordinal value given by that value attribute.

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one if the reversed is absent, or minus one if it is present.

The type attribute can be used to specify the kind of marker to use in the list, in the cases where that matters (e.g. because items are to be referenced by their number/letter). The attribute, if specified, must have a value that is a case-sensitive match for one of the characters given in the first cell of one of the rows of the following table. The type attribute represents the state given in the cell in the second column of the row whose first cell matches the attribute's value; if none of the cells match, or if the attribute is omitted, then the attribute represents the decimal state.

Keyword	State	Description	Examples for values 1-3 and 3999-4001
`1` (U+0031)	decimal	Decimal numbers	`1.`	`2.`	`3.`	...	`3999.`	`4000.`	`4001.`	...
`a` (U+0061)	lower-alpha	Lowercase latin alphabet	`a.`	`b.`	`c.`	...	`ewu.`	`ewv.`	`eww.`	...
`A` (U+0041)	upper-alpha	Uppercase latin alphabet	`A.`	`B.`	`C.`	...	`EWU.`	`EWV.`	`EWW.`	...
`i` (U+0069)	lower-roman	Lowercase roman numerals	`i.`	`ii.`	`iii.`	...	`mmmcmxcix.`	`i̅v̅.`	`i̅v̅i.`	...
`I` (U+0049)	upper-roman	Uppercase roman numerals	`I.`	`II.`	`III.`	...	`MMMCMXCIX.`	`I̅V̅.`	`I̅V̅I.`	...

User agents should render the items of the list in a manner consistent with the state of the type attribute of the ol element. Numbers less than or equal to zero should always use the decimal system regardless of the type attribute.

For CSS user agents, a mapping for this attribute to the 'list-style-type' CSS property is given in the rendering section (the mapping is straightforward: the states above have the same names as their corresponding CSS values).

The reversed, start, and type IDL attributes must reflect the respective content attributes of the same name. The start IDL attribute has the same default as its content attribute.

The following markup shows a list where the order matters, and where the ol element is therefore appropriate. Compare this list to the equivalent list in the ul section to see an example of the same items using the ul element.

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>Switzerland
 <li>United Kingdom
 <li>United States
 <li>Norway
</ol>

Note how changing the order of the list changes the meaning of the document. In the following example, changing the relative order of the first two items has changed the birthplace of the author:

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>United Kingdom
 <li>Switzerland
 <li>United States
 <li>Norway
</ol>

4.5.6 The `ul` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Zero or more li elements.

Content attributes:

DOM interface:

interface HTMLUListElement : HTMLElement {};

The ul element represents a list of items, where the order of the items is not important — that is, where changing the order would not materially change the meaning of the document.

The items of the list are the li element child nodes of the ul element.

The following markup shows a list where the order does not matter, and where the ul element is therefore appropriate. Compare this list to the equivalent list in the ol section to see an example of the same items using the ol element.

<p>I have lived in the following countries:</p>
<ul>
 <li>Norway
 <li>Switzerland
 <li>United Kingdom
 <li>United States
</ul>

Note that changing the order of the list does not change the meaning of the document. The items in the snippet above are given in alphabetical order, but in the snippet below they are given in order of the size of their current account balance in 2007, without changing the meaning of the document whatsoever:

<p>I have lived in the following countries:</p>
<ul>
 <li>Switzerland
 <li>Norway
 <li>United Kingdom
 <li>United States
</ul>

4.5.7 The `li` element

Categories

None.

Contexts in which this element can be used:

Inside ol elements.

Inside ul elements.

Inside menu elements.

Content model:

Content attributes:

If the element is a child of an ol element: value

DOM interface:

interface HTMLLIElement : HTMLElement {
           attribute long value;
};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

If the parent element is an ol element, then the li element has an ordinal value.

The value attribute, if present, must be a valid integer giving the ordinal value of the list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, the attribute must be treated as if it was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element (q.v.), if there is one. If there is not, the attribute has no effect.

The value IDL attribute must reflect the value of the value content attribute.

The following example, the top ten movies are listed (in reverse order). Note the way the list is given a title by using a figure element and its figcaption element.

<figure>
 <figcaption>The top 10 movies of all time</figcaption>
 <ol>
  <li value="10"><cite>Josie and the Pussycats</cite>, 2001</li>
  <li value="9"><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li value="8"><cite>A Bug's Life</cite>, 1998</li>
  <li value="7"><cite>Toy Story</cite>, 1995</li>
  <li value="6"><cite>Monsters, Inc</cite>, 2001</li>
  <li value="5"><cite>Cars</cite>, 2006</li>
  <li value="4"><cite>Toy Story 2</cite>, 1999</li>
  <li value="3"><cite>Finding Nemo</cite>, 2003</li>
  <li value="2"><cite>The Incredibles</cite>, 2004</li>
  <li value="1"><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

The markup could also be written as follows, using the reversed attribute on the ol element:

<figure>
 <figcaption>The top 10 movies of all time</figcaption>
 <ol reversed>
  <li><cite>Josie and the Pussycats</cite>, 2001</li>
  <li><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li><cite>A Bug's Life</cite>, 1998</li>
  <li><cite>Toy Story</cite>, 1995</li>
  <li><cite>Monsters, Inc</cite>, 2001</li>
  <li><cite>Cars</cite>, 2006</li>
  <li><cite>Toy Story 2</cite>, 1999</li>
  <li><cite>Finding Nemo</cite>, 2003</li>
  <li><cite>The Incredibles</cite>, 2004</li>
  <li><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

If the li element is the child of a menu element and itself has a child that defines a command, then the li element will match the :enabled and :disabled pseudo-classes in the same way as the first such child element does.

4.5.8 The `dl` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Zero or more groups each consisting of one or more dt elements followed by one or more dd elements.

Content attributes:

DOM interface:

interface HTMLDListElement : HTMLElement {};

The dl element represents an association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements). Within a single dl element, there should not be more than one dt element for each name.

Name-value groups may be terms and definitions, metadata topics and values, questions and answers, or any other groups of name-value data.

The values within a group are alternatives; multiple paragraphs forming part of the same value must all be given within the same dd element.

The order of the list of groups, and of the names and values within each group, may be significant.

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl.

If a dl element contains only dt elements, then it consists of one group with names but no values.

If a dl element contains only dd elements, then it consists of one group with values but no names.

If a dl element starts with one or more dd elements, then the first group has no associated name.

If a dl element ends with one or more dt elements, then the last group has no associated value.

When a dl element doesn't match its content model, it is often due to accidentally using dd elements in the place of dt elements and vice versa. Conformance checkers can spot such mistakes and might be able to advise authors how to correctly use the markup.

In the following example, one entry ("Authors") is linked to two values ("John" and "Luke").

<dl>
 <dt> Authors
 <dd> John
 <dd> Luke
 <dt> Editor
 <dd> Frank
</dl>

In the following example, one definition is linked to two terms.

<dl>
 <dt lang="en-US"> <dfn>color</dfn> </dt>
 <dt lang="en-GB"> <dfn>colour</dfn> </dt>
 <dd> A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. </dd>
</dl>

The following example illustrates the use of the dl element to mark up metadata of sorts. At the end of the example, one group has two metadata labels ("Authors" and "Editors") and two values ("Robert Rothman" and "Daniel Jackson").

<dl>
 <dt> Last modified time </dt>
 <dd> 2004-12-23T23:33Z </dd>
 <dt> Recommended update interval </dt>
 <dd> 60s </dd>
 <dt> Authors </dt>
 <dt> Editors </dt>
 <dd> Robert Rothman </dd>
 <dd> Daniel Jackson </dd>
</dl>

The following example shows the dl element used to give a set of instructions. The order of the instructions here is important (in the other examples, the order of the blocks was not important).

<p>Determine the victory points as follows (use the
first matching case):</p>
<dl>
 <dt> If you have exactly five gold coins </dt>
 <dd> You get five victory points </dd>
 <dt> If you have one or more gold coins, and you have one or more silver coins </dt>
 <dd> You get two victory points </dd>
 <dt> If you have one or more silver coins </dt>
 <dd> You get one victory point </dd>
 <dt> Otherwise </dt>
 <dd> You get no victory points </dd>
</dl>

The following snippet shows a dl element being used as a glossary. Note the use of dfn to indicate the word being defined.

<dl>
 <dt><dfn>Apartment</dfn>, n.</dt>
 <dd>An execution context grouping one or more threads with one or
 more COM objects.</dd>
 <dt><dfn>Flat</dfn>, n.</dt>
 <dd>A deflated tire.</dd>
 <dt><dfn>Home</dfn>, n.</dt>
 <dd>The user's login directory.</dd>
</dl>

The dl element is inappropriate for marking up dialogue. Examples of how to mark up dialogue are shown below.

4.5.9 The `dt` element

Categories: None.
Contexts in which this element can be used:: Before dd or dt elements inside dl elements.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

This example shows a list of frequently asked questions (a FAQ) marked up using the dt element for questions and the dd element for answers.

<article>
 <h1>FAQ</h1>
 <dl>
  <dt>What do we want?</dt>
  <dd>Our data.</dd>
  <dt>When do we want it?</dt>
  <dd>Now.</dd>
  <dt>Where is it?</dt>
  <dd>We are not sure.</dd>
 </dl>
</article>

4.5.10 The `dd` element

Categories: None.
Contexts in which this element can be used:: After dt or dd elements inside dl elements.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element).

A dl can be used to define a vocabulary list, like in a dictionary. In the following example, each entry, given by a dt with a dfn, has several dds, showing the various parts of the definition.

<dl>
 <dt><dfn>happiness</dfn></dt>
 <dd class="pronunciation">/'hæ p. nes/</dd>
 <dd class="part-of-speech"><i><abbr>n.</abbr></i></dd>
 <dd>The state of being happy.</dd>
 <dd>Good fortune; success. <q>Oh <b>happiness</b>! It worked!</q></dd>
 <dt><dfn>rejoice</dfn></dt>
 <dd class="pronunciation">/ri jois'/</dd>
 <dd><i class="part-of-speech"><abbr>v.intr.</abbr></i> To be delighted oneself.</dd>
 <dd><i class="part-of-speech"><abbr>v.tr.</abbr></i> To cause one to be delighted.</dd>
</dl>

4.5.11 The `figure` element

Categories: Flow content.; Sectioning root.
Contexts in which this element can be used:: Where flow content is expected.
Content model:: Either: One figcaption element followed by flow content.; Or: Flow content followed by one figcaption element.; Or: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The figure element represents some flow content, optionally with a caption, that is self-contained and is typically referenced as a single unit from the main flow of the document.

The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc, that are referred to from the main content of the document, but that could, without affecting the flow of the document, be moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix.

The first figcaption element child of the element, if any, represents the caption of the figure element's contents. If there is no child figcaption element, then there is no caption.

This example shows the figure element to mark up a code listing.

<p>In <a href="#l4">listing 4</a> we see the primary core interface
API declaration.</p>
<figure id="l4">
 <figcaption>Listing 4. The primary core interface API declaration.</figcaption>
 <pre><code>interface PrimaryCore {
 boolean verifyDataLine();
 void sendData(in sequence&lt;byte> data);
 void initSelfDestruct();
}</code></pre>
</figure>
<p>The API is designed to use UTF-8.</p>

Here we see a figure element to mark up a photo.

<figure>
 <img src="bubbles-work.jpeg"
      alt="Bubbles, sitting in his office chair, works on his
           latest project intently.">
 <figcaption>Bubbles at work</figcaption>
</figure>

In this example, we see an image that is not a figure, as well as an image and a video that are.

<h2>Malinko's comics</h2>

<p>This case centered on some sort of "intellectual property"
infringement related to a comic (see Exhibit A). The suit started
after a trailer ending with these words:

<blockquote>
 <img src="promblem-packed-action.png" alt="ROUGH COPY! Promblem-Packed Action!">
</blockquote>

<p>...was aired. A lawyer, armed with a Bigger Notebook, launched a
preemptive strike using snowballs. A complete copy of the trailer is
included with Exhibit B.

<figure>
 <img src="ex-a.png" alt="Two squiggles on a dirty piece of paper.">
 <figcaption>Exhibit A. The alleged <cite>rough copy</cite> comic.</figcaption>
</figure>

<figure>
 <video src="ex-b.mov"></video>
 <figcaption>Exhibit B. The <cite>Rough Copy</cite> trailer.</figcaption>
</figure>

<p>The case was resolved out of court.

Here, a part of a poem is marked up using figure.

<figure>
 <p>'Twas brillig, and the slithy toves<br>
 Did gyre and gimble in the wabe;<br>
 All mimsy were the borogoves,<br>
 And the mome raths outgrabe.</p>
 <figcaption><cite>Jabberwocky</cite> (first verse). Lewis Carroll, 1832-98</figcaption>
</figure>

In this example, which could be part of a much larger work discussing a castle, the figure has three images in it.

<figure>
 <img src="castle1423.jpeg" title="Etching. Anonymous, ca. 1423."
      alt="The castle has one tower, and a tall wall around it.">
 <img src="castle1858.jpeg" title="Oil-based paint on canvas. Maria Towle, 1858."
      alt="The castle now has two towers and two walls.">
 <img src="castle1999.jpeg" title="Film photograph. Peter Jankle, 1999."
      alt="The castle lies in ruins, the original tower all that remains in one piece.">
 <figcaption>The castle through the ages: 1423, 1858, and 1999 respectively.</figcaption>
</figure>

4.5.12 The `figcaption` element

Categories: None.
Contexts in which this element can be used:: As the first or last child of a figure element.
Content model:: Flow content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The figcaption element represents a caption or legend for the rest of the contents of the figcaption element's parent figure element, if any.

4.5.13 The `div` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Content attributes:

DOM interface:

interface HTMLDivElement : HTMLElement {};

The div element has no special meaning at all. It represents its children. It can be used with the class, lang, and title attributes to mark up semantics common to a group of consecutive elements.

Authors are strongly encouraged to view the div element as an element of last resort, for when no other element is suitable. Use of the div element instead of more appropriate elements leads to poor accessibility for readers and poor maintainability for authors.

For example, a blog post would be marked up using article, a chapter using section, a page's navigation aids using nav, and a group of form controls using fieldset.

On the other hand, div elements can be useful for stylistic purposes or to wrap multiple paragraphs within a section that are all to be annotated in a similar way. In the following example, we see div elements used as a way to set the language of two paragraphs at once, instead of setting the language on the two paragraph elements separately:

<article lang="en-US">
 <h1>My use of language and my cats</h1>
 <p>My cat's behavior hasn't changed much since her absence, except
 that she plays her new physique to the neighbors regularly, in an
 attempt to get pets.</p>
 <div lang="en-GB">
  <p>My other cat, coloured black and white, is a sweetie. He followed
  us to the pool today, walking down the pavement with us. Yesterday
  he apparently visited our neighbours. I wonder if he recognises that
  their flat is a mirror image of ours.</p>
  <p>Hm, I just noticed that in the last paragraph I used British
  English. But I'm supposed to write in American English. So I
  shouldn't say "pavement" or "flat" or "colour"...</p>
 </div>
 <p>I should say "sidewalk" and "apartment" and "color"!</p>
</article>

4.6 Text-level semantics

4.6.1 The `a` element

Categories

When the element only contains phrasing content: phrasing content.

Interactive content.

Contexts in which this element can be used:

When the element only contains phrasing content: where phrasing content is expected.

Otherwise: where flow content is expected.

Content model:

Transparent, but there must be no interactive content descendant.

Content attributes:

href

target

rel

media

hreflang

type

DOM interface:

interface HTMLAnchorElement : HTMLElement {
  stringifier attribute DOMString href;
           attribute DOMString target;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;

           attribute DOMString text;

  // URL decomposition IDL attributes
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
};

If the a element has an href attribute, then it represents a hyperlink (a hypertext anchor).

If the a element has no href attribute, then the element represents a placeholder for where a link might otherwise have been placed, if it had been relevant.

The target, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

If a site uses a consistent navigation toolbar on every page, then the link that would normally link to the page itself could be marked up using an a element:

<nav>
 <ul>
  <li> <a href="/">Home</a> </li>
  <li> <a href="/news">News</a> </li>
  <li> <a>Examples</a> </li>
  <li> <a href="/legal">Legal</a> </li>
 </ul>
</nav>

The href, target attributes affect what happens when users follow hyperlinks created using the a element. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The activation behavior of a elements that create hyperlinks is to run the following steps:

If the click event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the a element's target attribute is such that applying the rules for choosing a browsing context given a browsing context name, using the value of the target attribute as the browsing context name, would result in there not being a chosen browsing context, then raise an INVALID_ACCESS_ERR exception and abort these steps.
If the target of the click event is an img element with an ismap attribute specified, then server-side image map processing must be performed, as follows:
1. If the click event was a real pointing-device-triggered click event on the img element, then let x be the distance in CSS pixels from the left edge of the image's left border, if it has one, or the left edge of the image otherwise, to the location of the click, and let y be the distance in CSS pixels from the top edge of the image's top border, if it has one, or the top edge of the image otherwise, to the location of the click. Otherwise, let x and y be zero.
2. Let the hyperlink suffix be a U+003F QUESTION MARK character, the value of x expressed as a base-ten integer using ASCII digits, a U+002C COMMA character (,), and the value of y expressed as a base-ten integer using ASCII digits. ASCII digits are the characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
Finally, the user agent must follow the hyperlink created by the a element. If the steps above defined a hyperlink suffix, then take that into account when following the hyperlink.

a . text: Same as textContent.

The IDL attributes href, target, rel, media, hreflang, and type, must reflect the respective content attributes of the same name.

The IDL attribute relList must reflect the rel content attribute.

The text IDL attribute, on getting, must return the same value as the textContent IDL attribute on the element, and on setting, must act as if the textContent IDL attribute on the element had been set to the new value.

The a element also supports the complement of URL decomposition IDL attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition IDL attributes, with the input being the result of resolving the element's href attribute relative to the element, if there is such an attribute and resolving it is successful, or the empty string otherwise; and the common setter action being the same as setting the element's href attribute to the new output value.

The a element may be wrapped around entire paragraphs, lists, tables, and so forth, even entire sections, so long as there is no interactive content within (e.g. buttons or other links). This example shows how this can be used to make an entire advertising block into a link:

<aside class="advertising">
 <h1>Advertising</h1>
 <a href="http://ad.example.com/?adid=1929&amp;pubid=1422">
  <section>
   <h1>Mellblomatic 9000!</h1>
   <p>Turn all your widgets into mellbloms!</p>
   <p>Only $9.99 plus shipping and handling.</p>
  </section>
 </a>
 <a href="http://ad.example.com/?adid=375&amp;pubid=1422">
  <section>
   <h1>The Mellblom Browser</h1>
   <p>Web browsing at the speed of light.</p>
   <p>No other browser goes faster!</p>
  </section>
 </a>
</aside>

4.6.2 The `em` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particular piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

These examples show how changing the emphasis changes the meaning. First, a general statement of fact, with no emphasis:

<p>Cats are cute animals.</p>

By emphasizing the first word, the statement implies that the kind of animal under discussion is in question (maybe someone is asserting that dogs are cute):

<p><em>Cats</em> are cute animals.</p>

Moving the emphasis to the verb, one highlights that the truth of the entire sentence is in question (maybe someone is saying cats are not cute):

<p>Cats <em>are</em> cute animals.</p>

By moving it to the adjective, the exact nature of the cats is reasserted (maybe someone suggested cats were mean animals):

<p>Cats are <em>cute</em> animals.</p>

Similarly, if someone asserted that cats were vegetables, someone correcting this might emphasize the last word:

<p>Cats are cute <em>animals</em>.</p>

By emphasizing the entire sentence, it becomes clear that the speaker is fighting hard to get the point across. This kind of emphasis also typically affects the punctuation, hence the exclamation mark here.

<p><em>Cats are cute animals!</em></p>

Anger mixed with emphasizing the cuteness could lead to markup such as:

<p><em>Cats are <em>cute</em> animals!</em></p>

The em element isn't a generic "italics" element. Sometimes, text is intended to stand out from the rest of the paragraph, as if it was in a different mood or voice. For this, the i element is more appropriate.

The em element also isn't intended to convey importance; for that purpose, the strong element is more appropriate.

4.6.3 The `strong` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

Here is an example of a warning notice in a game, with the various parts marked up according to how important they are:

<p><strong>Warning.</strong> This dungeon is dangerous.
<strong>Avoid the ducks.</strong> Take any gold you find.
<strong><strong>Do not take any of the diamonds</strong>,
they are explosive and <strong>will destroy anything within
ten meters.</strong></strong> You have been warned.</p>

4.6.4 The `small` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The small element represents side comments such as small print.

Small print typically features disclaimers, caveats, legal restrictions, or copyrights. Small print is also sometimes used for attribution, or for satisfying licensing requirements.

The small element does not "de-emphasize" or lower the importance of text emphasized by the em element or marked as important with the strong element. To mark text as not emphasized or important, simply do not mark it up with the em or strong elements respectively.

The small element should not be used for extended spans of text, such as multiple paragraphs, lists, or sections of text. It is only intended for short runs of text. The text of a page listing terms of use, for instance, would not be a suitable candidate for the small element: in such a case, the text is not a side comment, it is the main content of the page.

In this example, the small element is used to indicate that value-added tax is not included in a price of a hotel room:

<dl>
 <dt>Single room
 <dd>199 € <small>breakfast included, VAT not included</small>
 <dt>Double room
 <dd>239 € <small>breakfast included, VAT not included</small>
</dl>

In this second example, the small element is used for a side comment in an article.

<p>Example Corp today announced record profits for the
second quarter <small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)</small>, leading to speculation about a third quarter
merger with Demo Group.</p>

This is distinct from a sidebar, which might be multiple paragraphs long and is removed from the main flow of text. In the following example, we see a sidebar from the same article. This sidebar also has small print, indicating the source of the information in the sidebar.

<aside>
 <h1>Example Corp</h1>
 <p>This company mostly creates small software and Web
 sites.</p>
 <p>The Example Corp company mission is "To provide entertainment
 and news on a sample basis".</p>
 <p><small>Information obtained from <a
 href="http://example.com/about.html">example.com</a> home
 page.</small></p>
</aside>

In this last example, the small element is marked as being important small print.

<p><strong><small>Continued use of this service will result in a kiss.</small></strong></p>

4.6.5 The `s` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The s element represents contents that are no longer accurate or no longer relevant.

The s element is not appropriate when indicating document edits; to mark a span of text as having been removed from a document, use the del element.

In this example a recommended retail price has been marked as no longer relevant as the product in question has a new sale price.

<p>Buy our Iced Tea and Lemonade!</p>
<p><s>Recommended retail price: $3.99 per bottle</s></p>
<p><strong>Now selling for just $2.99 a bottle!</strong></p>

4.6.6 The `cite` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The cite element represents the title of a work (e.g. a book, a paper, an essay, a poem, a score, a song, a script, a film, a TV show, a game, a sculpture, a painting, a theatre production, a play, an opera, a musical, an exhibition, a legal case report, etc). This can be a work that is being quoted or referenced in detail (i.e. a citation), or it can just be a work that is mentioned in passing.

A person's name is not the title of a work — even if people call that person a piece of work — and the element must therefore not be used to mark up people's names. (In some cases, the b element might be appropriate for names; e.g. in a gossip article where the names of famous people are keywords rendered with a different style to draw attention to them. In other cases, if an element is really needed, the span element can be used.)

This next example shows a typical use of the cite element:

<p>My favorite book is <cite>The Reality Dysfunction</cite> by
Peter F. Hamilton. My favorite comic is <cite>Pearls Before
Swine</cite> by Stephan Pastis. My favorite track is <cite>Jive
Samba</cite> by the Cannonball Adderley Sextet.</p>

This is correct usage:

<p>According to the Wikipedia article <cite>HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The following, however, is incorrect usage, as the cite element here is containing far more than the title of the work:

<!-- do not copy this example, it is an example of bad usage! -->
<p>According to <cite>the Wikipedia article on HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The cite element is obviously a key part of any citation in a bibliography, but it is only used to mark the title:

<p><cite>Universal Declaration of Human Rights</cite>, United Nations,
December 1948. Adopted by General Assembly resolution 217 A (III).</p>

A citation is not a quote (for which the q element is appropriate).

This is incorrect usage, because cite is not for quotes:

<p><cite>This is wrong!</cite>, said Ian.</p>

This is also incorrect usage, because a person is not a work:

<p><q>This is still wrong!</q>, said <cite>Ian</cite>.</p>

The correct usage does not use a cite element:

<p><q>This is correct</q>, said Ian.</p>

As mentioned above, the b element might be relevant for marking names as being keywords in certain kinds of documents:

<p>And then <b>Ian</b> said <q>this might be right, in a
gossip column, maybe!</q>.</p>

4.6.7 The `q` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; cite
DOM interface:: Uses HTMLQuoteElement.

The q element represents some phrasing content quoted from another source.

Quotation punctuation (such as quotation marks) that is quoting the contents of the element must not appear immediately before, after, or inside q elements; they will be inserted into the rendering by the user agent.

Content inside a q element must be quoted from another source, whose address, if it has one, may be cited in the cite attribute. The source may be fictional, as when quoting characters in a novel or screenplay.

The q element must not be used in place of quotation marks that do not represent quotes; for example, it is inappropriate to use the q element for marking up sarcastic statements.

The use of q elements to mark up quotations is entirely optional; using explicit quotation punctuation without q elements is just as correct.

Here is a simple example of the use of the q element:

<p>The man said <q>Things that are impossible just take
longer</q>. I disagreed with him.</p>

Here is an example with both an explicit citation link in the q element, and an explicit citation outside:

<p>The W3C page <cite>About W3C</cite> says the W3C's
mission is <q cite="http://www.w3.org/Consortium/">To lead the
World Wide Web to its full potential by developing protocols and
guidelines that ensure long-term growth for the Web</q>. I
disagree with this mission.</p>

In the following example, the quotation itself contains a quotation:

<p>In <cite>Example One</cite>, he writes <q>The man
said <q>Things that are impossible just take longer</q>. I
disagreed with him</q>. Well, I disagree even more!</p>

In the following example, quotation marks are used instead of the q element:

<p>His best argument was ❝I disagree❞, which
I thought was laughable.</p>

In the following example, there is no quote — the quotation marks are used to name a word. Use of the q element in this case would be inappropriate.

<p>The word "ineffable" could have been used to describe the disaster
resulting from the campaign's mismanagement.</p>

4.6.8 The `dfn` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content, but there must be no dfn element descendants.
Content attributes:: Global attributes; Also, the title attribute has special semantics on this element.
DOM interface:: Uses HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that is the nearest ancestor of the dfn element must also contain the definition(s) for the term given by the dfn element.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must contain only the term being defined.

The title attribute of ancestor elements does not affect dfn elements.

An a element that links to a dfn element represents an instance of the term defined by the dfn element.

In the following fragment, the term "GDO" is first defined in the first paragraph, then used in the second.

<p>The <dfn><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <abbr title="Garage Door Opener">GDO</abbr>
and so Hammond ordered the iris to be opened.</p>

With the addition of an a element, the reference can be made explicit:

<p>The <dfn id=gdo><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <a href=#gdo><abbr title="Garage Door Opener">GDO</abbr></a>
and so Hammond ordered the iris to be opened.</p>

4.6.9 The `abbr` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; Also, the title attribute has special semantics on this element.
DOM interface:: Uses HTMLElement.

The abbr element represents an abbreviation or acronym, optionally with its expansion. The title attribute may be used to provide an expansion of the abbreviation. The attribute, if specified, must contain an expansion of the abbreviation, and nothing else.

The paragraph below contains an abbreviation marked up with the abbr element. This paragraph defines the term "Web Hypertext Application Technology Working Group".

<p>The <dfn id=whatwg><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></dfn>
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

An alternative way to write this would be:

<p>The <dfn id=whatwg>Web Hypertext Application Technology
Working Group</dfn> (<abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr>)
is a loose unofficial collaboration of Web browser manufacturers and
interested parties who wish to develop new technologies designed to
allow authors to write and deploy Applications over the World Wide
Web.</p>

This paragraph has two abbreviations. Notice how only one is defined; the other, with no expansion associated with it, does not use the abbr element.

<p>The
<abbr title="Web Hypertext Application Technology Working Group">WHATWG</abbr>
started working on HTML5 in 2004.</p>

This paragraph links an abbreviation to its definition.

<p>The <a href="#whatwg"><abbr
title="Web Hypertext Application Technology Working Group">WHATWG</abbr></a>
community does not have much representation from Asia.</p>

This paragraph marks up an abbreviation without giving an expansion, possibly as a hook to apply styles for abbreviations (e.g. smallcaps).

<p>Philip` and Dashiva both denied that they were going to
get the issue counts from past revisions of the specification to
backfill the <abbr>WHATWG</abbr> issue graph.</p>

If an abbreviation is pluralized, the expansion's grammatical number (plural vs singular) must match the grammatical number of the contents of the element.

Here the plural is outside the element, so the expansion is in the singular:

<p>Two <abbr title="Working Group">WG</abbr>s worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Here the plural is inside the element, so the expansion is in the plural:

<p>Two <abbr title="Working Groups">WGs</abbr> worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Abbreviations do not have to be marked up using this element. It is expected to be useful in the following cases:

Abbreviations for which the author wants to give expansions, where using the abbr element with a title attribute is an alternative to including the expansion inline (e.g. in parentheses).
Abbreviations that are likely to be unfamiliar to the document's readers, for which authors are encouraged to either mark up the abbreviation using a abbr element with a title attribute or include the expansion inline in the text the first time the abbreviation is used.
Abbreviations whose presence needs to be semantically annotated, e.g. so that they can be identified from a style sheet and given specific styles, for which the abbr element can be used without a title attribute.

Providing an expansion in a title attribute once will not necessarily cause other abbr elements in the same document with the same contents but without a title attribute to behave as if they had the same expansion. Every abbr element is independent.

4.6.10 The `time` element

Categories

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Phrasing content, but there must be no time element descendants.

Content attributes:

datetime

pubdate

DOM interface:

interface HTMLTimeElement : HTMLElement {
           attribute DOMString dateTime;
           attribute boolean pubDate;
  readonly attribute Date valueAsDate;
};

The time element represents either a time on a 24 hour clock, or a precise date in the proleptic Gregorian calendar, optionally with a time and a time-zone offset. [GREGORIAN]

This element is intended as a way to encode modern dates and times in a machine-readable way so that, for example, user agents can offer to add birthday reminders or scheduled events to the user's calendar.

The time element is not intended for encoding times for which a precise date or time cannot be established. For example, it would be inappropriate for encoding times like "one millisecond after the big bang", "the early part of the Jurassic period", or "a winter around 250 BCE".

For dates before the introduction of the Gregorian calendar, authors are encouraged to not use the time element, or else to be very careful about converting dates and times from the period to the Gregorian calendar. This is complicated by the manner in which the Gregorian calendar was phased in, which occurred at different times in different countries, ranging from partway through the 16th century all the way to early in the 20th.

The pubdate attribute is a boolean attribute. If specified, it indicates that the date and time given by the element is the publication date and time of the nearest ancestor article element, or, if the element has no ancestor article element, of the document as a whole. If the element has a pubdate attribute specified, then the element needs a date. For each article element, there must be no more than one time element with a pubdate attribute whose nearest ancestor is that article element. Furthermore, for each Document, there must be no more than one time element with a pubdate attribute that does not have an ancestor article element.

The datetime attribute, if present, gives the date or time being specified. Otherwise, the date or time is given by the element's contents.

If the element needs a date, and the datetime attribute is present, then the attribute's value must be a valid date string with optional time.

If the element needs a date, but the datetime attribute is not present, then the element's textContent must be a valid date string in content with optional time.

If the element does not need a date, and the datetime attribute is present, then the attribute's value must be a valid date or time string.

If the element does not need a date, but the datetime attribute is not present, then the element's textContent must be a valid date or time string in content.

The date, if any, must be expressed using the Gregorian calendar.

If the datetime attribute is present, the user agent should convey the attribute's value to the user when rendering the element.

The time element can be used to encode dates, for example in Microformats. The following shows a hypothetical way of encoding an event using a variant on hCalendar that uses the time element:

<div class="vevent">
 <a class="url" href="http://www.web2con.com/">http://www.web2con.com/</a>
  <span class="summary">Web 2.0 Conference</span>:
  <time class="dtstart" datetime="2007-10-05">October 5</time> -
  <time class="dtend" datetime="2007-10-20">19</time>,
  at the <span class="location">Argent Hotel, San Francisco, CA</span>
 </div>

(The end date is encoded as one day after the last date of the event because in the iCalendar format, end dates are exclusive, not inclusive.)

The time element is not necessary for encoding dates or times. In the following snippet, the time is encoded using time, so that it can be restyled (e.g. using XBL2) to match local conventions, while the year is not marked up at all, since marking it up would not be particularly useful, and doing so is thus not allowed.

<p>I usually have a snack at <time>16:00</time>.</p>
<p>I've liked model trains since at least 1983.</p>

Using a styling technology that supports restyling times, the first paragraph from the above snippet could be rendered as follows:

I usually have a snack at 4pm.

Or it could be rendered as follows:

I usually have a snack at 16h00.

The dateTime IDL attribute must reflect the datetime content attribute.

The pubDate IDL attribute must reflect the pubdate content attribute.

User agents, to obtain the date, time, and time-zone offset represented by a time element, must follow these steps:

If the datetime attribute is present, then use the rules to parse a date or time string with the flag in attribute from the value of that attribute, and let the result be result.
Otherwise, use the rules to parse a date or time string with the flag in content from the element's textContent, and let the result be result.
If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the time-zone offset is unknown.
Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a time-zone offset, then the time-zone offset is the element's time-zone offset. (A time-zone offset can only be present if both a date and a time are also present.)

time . valueAsDate: Returns a Date object representing the specified date and time.

The valueAsDate IDL attribute must return either null or a new Date object initialised to the relevant value as defined by the following list:

If the date is known but the time is not: The time corresponding to midnight UTC (i.e. the first second) of the given date.
If the time is known but the date is not: The time corresponding to the given time of 1970-01-01, with the time zone UTC.
If both the date and the time are known: The time corresponding to the date and time, with the given time-zone offset.
If neither the date nor the time are known: The null value.

When a Date object is to be returned, a new one must be constructed.

In the following snippet:

<p>Our first date was <time datetime="2006-09-23">a Saturday</time>.</p>

...the time element's valueAsDate attribute would have the value 1,158,969,600,000ms.

In the following snippet:

<p>Many people get up at <time>08:00</time>.</p>

...the time element's valueAsDate attribute would have the value 28,800,000ms.

In this example, an article's publication date is marked up using time:

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate>2009-08-30</time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

Here is another way that could be marked up. In this example, legacy user agents would say "today", while newer user agents would render the time in a locale-specific manner based on the value of the attribute.

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate datetime="2009-08-30">today</time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

Here is the same thing but with the time included only. Because the element is empty, legacy user agents will not show anything useful; user agents that implement this specification, on the other hand, would show the date and time in a locale-specific manner.

<article>
 <h1>Small tasks</h1>
 <footer>Published <time pubdate datetime="2009-08-30T07:13Z"></time>.</footer>
 <p>I put a bike bell on his bike.</p>
</article>

4.6.11 The `code` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The code element represents a fragment of computer code. This could be an XML element name, a filename, a computer program, or any other string that a computer would recognize.

Although there is no formal way to indicate the language of computer code being marked up, authors who wish to mark code elements with the language used, e.g. so that syntax highlighting scripts can use the right rules, may do so by adding a class prefixed with "language-" to the element.

The following example shows how the element can be used in a paragraph to mark up element names and computer code, including punctuation.

<p>The <code>code</code> element represents a fragment of computer
code.</p>

<p>When you call the <code>activate()</code> method on the
<code>robotSnowman</code> object, the eyes glow.</p>

<p>The example below uses the <code>begin</code> keyword to indicate
the start of a statement block. It is paired with an <code>end</code>
keyword, which is followed by the <code>.</code> punctuation character
(full stop) to indicate the end of the program.</p>

The following example shows how a block of code could be marked up using the pre and code elements.

<pre><code class="language-pascal">var i: Integer;
begin
   i := 1;
end.</code></pre>

A class is used in that example to indicate the language used.

See the pre element for more details.

4.6.12 The `var` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, or it could just be a term used as a placeholder in prose.

In the paragraph below, the letter "n" is being used as a variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavors of ice cream to be available for purchase!</p>

For mathematics, in particular for anything beyond the simplest of expressions, MathML is more appropriate. However, the var element can still be used to refer to specific variables that are then mentioned in MathML expressions.

In this example, an equation is shown, with a legend that references the variables in the equation. The expression itself is marked up with MathML, but the variables are mentioned in the figure's legend using var.

<figure>
 <math>
  <mi>a</mi>
  <mo>=</mo>
  <msqrt>
   <msup><mi>b</mi><mn>2</mn></msup>
   <mi>+</mi>
   <msup><mi>c</mi><mn>2</mn></msup>
  </msqrt>
 </math>
 <figcaption>
  Using Pythagoras' theorem to solve for the hypotenuse <var>a</var> of
  a triangle with sides <var>b</var> and <var>c</var>
 </figcaption>
</figure>

4.6.13 The `samp` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The samp element represents (sample) output from a program or computing system.

See the pre and kbd elements for more details.

This example shows the samp element being used inline:

<p>The computer said <samp>Too much cheese in tray
two</samp> but I didn't know what that meant.</p>

This second example shows a block of sample output. Nested samp and kbd elements allow for the styling of specific elements of the sample output using a style sheet.

<pre><samp><span class="prompt">jdoe@mowmow:~$</span> <kbd>ssh demo.example.com</kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

<span class="prompt">jdoe@demo:~$</span> <span class="cursor">_</span></samp></pre>

4.6.14 The `kbd` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).

When the kbd element is nested inside a samp element, it represents the input as it was echoed by the system.

When the kbd element contains a samp element, it represents input based on system output, for example invoking a menu item.

When the kbd element is nested inside another kbd element, it represents an actual key or other single unit of input as appropriate for the input mechanism.

Here the kbd element is used to indicate keys to press:

<p>To make George eat an apple, press <kbd><kbd>Shift</kbd>+<kbd>F3</kbd></kbd></p>

In this second example, the user is told to pick a particular menu item. The outer kbd element marks up a block of input, with the inner kbd elements representing each individual step of the input, and the samp elements inside them indicating that the steps are input based on something being displayed by the system, in this case menu labels:

<p>To make George eat an apple, select
    <kbd><kbd><samp>File</samp></kbd>|<kbd><samp>Eat Apple...</samp></kbd></kbd>
</p>

Such precision isn't necessary; the following is equally fine:

<p>To make George eat an apple, select <kbd>File | Eat Apple...</kbd></p>

4.6.15 The `sub` and `sup` elements

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Use HTMLElement.

The sup element represents a superscript and the sub element represents a subscript.

These elements must be used only to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the sub and sup elements to be used in the name of the LaTeX document preparation system. In general, authors should use these elements only if the absence of those elements would change the meaning of the content.

In certain languages, superscripts are part of the typographical conventions for some abbreviations.

<p>The most beautiful women are
<span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and
<span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>

The sub element can be used inside a var element, for variables that have subscripts.

Here, the sub element is used to represents the subscript that identifies the variable in a family of variables:

<p>The coordinate of the <var>i</var>th point is
(<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>).
For example, the 10th point has coordinate
(<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>

Mathematical expressions often use subscripts and superscripts. Authors are encouraged to use MathML for marking up mathematics, but authors may opt to use sub and sup if detailed mathematical markup is not desired. [MATHML]

<var>E</var>=<var>m</var><var>c</var><sup>2</sup>

f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>

4.6.16 The `i` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose in a manner indicating a different quality of text, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, or a ship name in Western texts.

Terms in languages different from the main text should be annotated with lang attributes (or, in XML, lang attributes in the XML namespace).

The examples below show uses of the i element:

<p>The <i class="taxonomy">Felis silvestris catus</i> is cute.</p>
<p>The term <i>prose content</i> is defined above.</p>
<p>There is a certain <i lang="fr">je ne sais quoi</i> in the air.</p>

In the following example, a dream sequence is marked up using i elements.

<p>Raymond tried to sleep.</p>
<p><i>The ship sailed away on Thursday</i>, he
dreamt. <i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.</i></p>
<p><i>Finally one night he picked up the courage to speak with
her—</i></p>
<p>Raymond woke with a start as the fire alarm rang out.</p>

Authors can use the class attribute on the i element to identify why the element is being used, so that if the style of a particular use (e.g. dream sequences as opposed to taxonomic terms) is to be changed at a later date, the author doesn't have to go through the entire document (or series of related documents) annotating each use.

Authors are encouraged to consider whether other elements might be more applicable than the i element, for instance the em element for marking up stress emphasis, or the dfn element to mark up the defining instance of a term.

Style sheets can be used to format i elements, just like any other element can be restyled. Thus, it is not the case that content in i elements will necessarily be italicized.

4.6.17 The `b` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The b element represents a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede.

The following example shows a use of the b element to highlight key words without marking them up as important:

<p>The <b>frobonitor</b> and <b>barbinator</b> components are fried.</p>

In the following example, objects in a text adventure are highlighted as being special by use of the b element.

<p>You enter a small room. Your <b>sword</b> glows
brighter. A <b>rat</b> scurries past the corner wall.</p>

Another case where the b element is appropriate is in marking up the lede (or lead) sentence or paragraph. The following example shows how a BBC article about kittens adopting a rabbit as their own could be marked up:

<article>
 <h2>Kittens 'adopted' by pet rabbit</h2>
 <p><b class="lede">Six abandoned kittens have found an
 unexpected new mother figure — a pet rabbit.</b></p>
 <p>Veterinary nurse Melanie Humble took the three-week-old
 kittens to her Aberdeen home.</p>
[...]

As with the i element, authors can use the class attribute on the b element to identify why the element is being used, so that if the style of a particular use is to be changed at a later date, the author doesn't have to go through annotating each use.

The b element should be used as a last resort when no other element is more appropriate. In particular, headings should use the h1 to h6 elements, stress emphasis should use the em element, importance should be denoted with the strong element, and text marked or highlighted should use the mark element.

The following would be incorrect usage:

<p><b>WARNING!</b> Do not frob the barbinator!</p>

In the previous example, the correct element to use would have been strong, not b.

Style sheets can be used to format b elements, just like any other element can be restyled. Thus, it is not the case that content in b elements will necessarily be boldened.

4.6.18 The `u` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The u element represents a span of text with an unarticulated, though explicitly rendered, non-textual annotation, such as labeling the text as being a proper name in Chinese text (a Chinese proper name mark), or labeling the text as being misspelt.

In most cases, another element is likely to be more appropriate: for marking stress emphasis, the em element should be used; for marking key words or phrases either the b element or the mark element should be used, depending on the context; for marking book titles, the cite element should be used; for labeling text with explicit textual annotations, the ruby element should be used; for labeling ship names in Western texts, the i element should be used.

The default rendering of the u element in visual presentations clashes with the conventional rendering of hyperlinks (underlining). Authors are encouraged to avoid using the u element where it could be confused for a hyperlink.

4.6.19 The `mark` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The mark element represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context. When used in a quotation or other block of text referred to from the prose, it indicates a highlight that was not originally present but which has been added to bring the reader's attention to a part of the text that might not have been considered important by the original author when the block was originally written, but which is now under previously unexpected scrutiny. When used in the main prose of a document, it indicates a part of the document that has been highlighted due to its likely relevance to the user's current activity.

This example shows how the mark element can be used to bring attention to a particular part of a quotation:

<p lang="en-US">Consider the following quote:</p>
<blockquote lang="en-GB">
 <p>Look around and you will find, no-one's really
 <mark>colour</mark> blind.</p>
</blockquote>
<p lang="en-US">As we can tell from the <em>spelling</em> of the word,
the person writing this quote is clearly not American.</p>

(If the goal was to mark the element as misspelt, however, the u element, possibly with a class, would be more appropriate.

Another example of the mark element is highlighting parts of a document that are matching some search string. If someone looked at a document, and the server knew that the user was searching for the word "kitten", then the server might return the document with one paragraph modified as follows:

<p>I also have some <mark>kitten</mark>s who are visiting me
these days. They're really cute. I think they like my garden! Maybe I
should adopt a <mark>kitten</mark>.</p>

In the following snippet, a paragraph of text refers to a specific part of a code fragment.

<p>The highlighted part below is where the error lies:</p>
<pre><code>var i: Integer;
begin
   i := <mark>1.1</mark>;
end.</code></pre>

This is separate from syntax highlighting, for which span is more appropriate. Combining both, one would get:

<p>The highlighted part below is where the error lies:</p>
<pre><code><span class=keyword>var</span> <span class=ident>i</span>: <span class=type>Integer</span>;
<span class=keyword>begin</span>
   <span class=ident>i</span> := <span class=literal><mark>1.1</mark></span>;
<span class=keyword>end</span>.</code></pre>

This is another example showing the use of mark to highlight a part of quoted text that was originally not emphasized. In this example, common typographic conventions have led the author to explicitly style mark elements in quotes to render in italics.

<article>
 <style scoped>
  blockquote mark, q mark {
    font: inherit; font-style: italic;
    text-decoration: none;
    background: transparent; color: inherit;
  }
  .bubble em {
    font: inherit; font-size: larger;
    text-decoration: underline;
  }
 </style>
 <h1>She knew</h1>
 <p>Did you notice the subtle joke in the joke on panel 4?</p>
 <blockquote>
  <p class="bubble">I didn't <em>want</em> to believe. <mark>Of course
  on some level I realized it was a known-plaintext attack.</mark> But I
  couldn't admit it until I saw for myself.</p>
 </blockquote>
 <p>(Emphasis mine.) I thought that was great. It's so pedantic, yet it
 explains everything neatly.</p>
</article>

Note, incidentally, the distinction between the em element in this example, which is part of the original text being quoted, and the mark element, which is highlighting a part for comment.

The following example shows the difference between denoting the importance of a span of text (strong) as opposed to denoting the relevance of a span of text (mark). It is an extract from a textbook, where the extract has had the parts relevant to the exam highlighted. The safety warnings, important though they may be, are apparently not relevant to the exam.

<h3>Wormhole Physics Introduction</h3>

<p><mark>A wormhole in normal conditions can be held open for a
maximum of just under 39 minutes.</mark> Conditions that can increase
the time include a powerful energy source coupled to one or both of
the gates connecting the wormhole, and a large gravity well (such as a
black hole).</p>

<p><mark>Momentum is preserved across the wormhole. Electromagnetic
radiation can travel in both directions through a wormhole,
but matter cannot.</mark></p>

<p>When a wormhole is created, a vortex normally forms.
<strong>Warning: The vortex caused by the wormhole opening will
annihilate anything in its path.</strong> Vortexes can be avoided when
using sufficiently advanced dialing technology.</p>

<p><mark>An obstruction in a gate will prevent it from accepting a
wormhole connection.</mark></p>

4.6.20 The `ruby` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: One or more groups of: phrasing content followed either by a single rt element, or an rp element, an rt element, and another rp element.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The ruby element allows one or more spans of phrasing content to be marked with ruby annotations. Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations. In Japanese, this form of typography is also known as furigana.

A ruby element represents the spans of phrasing content it contains, ignoring all the child rt and rp elements and their descendants. Those spans of phrasing content have associated annotations created using the rt element.

In this example, each ideograph in the Japanese text 漢字 is annotated with its reading in hiragana.

...
<ruby>漢<rt>かん</rt>字<rt>じ　</rt></ruby>
...

This might be rendered as:

The two main ideographs, each with its annotation in hiragana rendered in a smaller font above it.

In this example, each ideograph in the traditional Chinese text 漢字 is annotated with its bopomofo reading.

<ruby>漢<rt>ㄏㄢˋ</rt>字<rt>ㄗˋ　</rt></ruby>

This might be rendered as:

The two main ideographs, each with its bopomofo annotation rendered in a smaller font next to it.

In this example, each ideograph in the simplified Chinese text 汉字 is annotated with its pinyin reading.

...<ruby>汉<rt>hàn</rt>字<rt>zì </rt></ruby>...

This might be rendered as:

The two main ideographs, each with its pinyin annotation rendered in a smaller font above it.

4.6.21 The `rt` element

Categories: None.
Contexts in which this element can be used:: As a child of a ruby element.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The rt element marks the ruby text component of a ruby annotation.

An rt element that is a child of a ruby element represents an annotation (given by its children) for the zero or more nodes of phrasing content that immediately precedes it in the ruby element, ignoring rp elements.

An rt element that is not a child of a ruby element represents the same thing as its children.

4.6.22 The `rp` element

Categories: None.
Contexts in which this element can be used:: As a child of a ruby element, either immediately before or immediately after an rt element.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The rp element can be used to provide parentheses around a ruby text component of a ruby annotation, to be shown by user agents that don't support ruby annotations.

An rp element that is a child of a ruby element represents nothing and its contents must be ignored. An rp element whose parent element is not a ruby element represents its children.

The example above, in which each ideograph in the text 漢字 is annotated with its phonetic reading, could be expanded to use rp so that in legacy user agents the readings are in parentheses:

...
<ruby>
 漢 <rp>(</rp><rt>かん</rt><rp>)</rp>
 字 <rp>(</rp><rt>じ</rt><rp>)</rp>
</ruby>
...

In conforming user agents the rendering would be as above, but in user agents that do not support ruby, the rendering would be:

... 漢 (かん) 字 (じ) ...

4.6.23 The `bdi` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; Also, the dir global attribute has special semantics on this element.
DOM interface:: Uses HTMLElement.

The bdi element represents a span of text that is to be isolated from its surroundings for the purposes of bidirectional text formatting. [BIDI]

The dir global attribute defaults to auto on this element (it never inherits from the parent element like with other elements).

For the purposes of applying the bidirectional algorithm to the contents of a bdi element, user agents must treat the element as a paragraph-level container.

For the purposes of applying the bidirectional algorithm to the paragraph-level container that a bdi element finds itself within, the bdi element must be treated like a U+FFFC OBJECT REPLACEMENT CHARACTER (in the same manner that an image or other inline object is handled).

The requirements on handling the bdi element for the bidirectional algorithm may be implemented indirectly through the style layer. For example, an HTML+CSS user agent could implement these requirements by implementing the CSS 'unicode-bidi' property. [CSS]

This element is especially useful when embedding user-generated content with an unknown directionality.

In this example, usernames are shown along with the number of posts that the user has submitted. If the bdi element were not used, the username of the Arabic user would end up confusing the text (the bidirectional algorithm would put the colon and the number "3" next to the word "User" rather than next to the word "posts").

<ul>
 <li>User <bdi>jcranmer</bdi>: 12 posts.
 <li>User <bdi>hober</bdi>: 5 posts.
 <li>User <bdi>إيان</bdi>: 3 posts.
</ul>

4.6.24 The `bdo` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; Also, the dir global attribute has special semantics on this element.
DOM interface:: Uses HTMLElement.

The bdo element represents explicit text directionality formatting control for its children. It allows authors to override the Unicode bidirectional algorithm by explicitly specifying a direction override. [BIDI]

Authors must specify the dir attribute on this element, with the value ltr to specify a left-to-right override and with the value rtl to specify a right-to-left override.

If the element's dir attribute is in the rtl state, then for the purposes of the bidirectional algorithm, the user agent must act as if there was a U+202D LEFT-TO-RIGHT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

If the element's dir attribute is in the ltr, then for the purposes of the bidirectional algorithm, the user agent must act as if there was a U+202E RIGHT-TO-LEFT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

The requirements on handling the bdo element for the bidirectional algorithm may be implemented indirectly through the style layer. For example, an HTML+CSS user agent could implement these requirements by implementing the CSS 'unicode-bidi' property. [CSS]

4.6.25 The `span` element

Categories

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Content attributes:

DOM interface:

interface HTMLSpanElement : HTMLElement {};

The span element doesn't mean anything on its own, but can be useful when used together with the global attributes, e.g. class, lang, or dir. It represents its children.

In this example, a code fragment is marked up using span elements and class attributes so that its keywords and identifiers can be color-coded from CSS:

<pre><code class="lang-c"><span class="keyword">for</span> (<span class="ident">j</span> = 0; <span class="ident">j</span> &lt; 256; <span class="ident">j</span>++) {
  <span class="ident">i_t3</span> = (<span class="ident">i_t3</span> & 0x1ffff) | (<span class="ident">j</span> &lt;&lt; 17);
  <span class="ident">i_t6</span> = (((((((<span class="ident">i_t3</span> >> 3) ^ <span class="ident">i_t3</span>) >> 1) ^ <span class="ident">i_t3</span>) >> 8) ^ <span class="ident">i_t3</span>) >> 5) & 0xff;
  <span class="keyword">if</span> (<span class="ident">i_t6</span> == <span class="ident">i_t1</span>)
    <span class="keyword">break</span>;
}</code></pre>

4.6.26 The `br` element

Categories

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Empty.

Content attributes:

DOM interface:

interface HTMLBRElement : HTMLElement {};

The br element represents a line break.

While line breaks are usually represented in visual media by physically moving subsequent text to a new line, a style sheet or user agent would be equally justified in causing line breaks to be rendered in a different manner, for instance as green dots, or as extra spacing.

br elements must be used only for line breaks that are actually part of the content, as in poems or addresses.

The following example is correct usage of the br element:

<p>P. Sherman<br>
42 Wallaby Way<br>
Sydney</p>

br elements must not be used for separating thematic groups in a paragraph.

The following examples are non-conforming, as they abuse the br element:

<p><a ...>34 comments.</a><br>
<a ...>Add a comment.</a></p>

<p><label>Name: <input name="name"></label><br>
<label>Address: <input name="address"></label></p>

Here are alternatives to the above, which are correct:

<p><a ...>34 comments.</a></p>
<p><a ...>Add a comment.</a></p>

<p><label>Name: <input name="name"></label></p>
<p><label>Address: <input name="address"></label></p>

If a paragraph consists of nothing but a single br element, it represents a placeholder blank line (e.g. as in a template). Such blank lines must not be used for presentation purposes.

Any content inside br elements must not be considered part of the surrounding text.

A br element should separate paragraphs for the purposes of the Unicode bidirectional algorithm. This requirement may be implemented indirectly through the style layer. For example, an HTML+CSS user agent could implement these requirements by implementing the CSS 'unicode-bidi' property. [BIDI] [CSS]

4.6.27 The `wbr` element

Categories: Flow content.; Phrasing content.
Contexts in which this element can be used:: Where phrasing content is expected.
Content model:: Empty.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The wbr element represents a line break opportunity.

In the following example, someone is quoted as saying something which, for effect, is written as one long word. However, to ensure that the text can be wrapped in a readable fashion, the individual words in the quote are separated using a wbr element.

<p>So then he pointed at the tiger and screamed
"there<wbr>is<wbr>no<wbr>way<wbr>you<wbr>are<wbr>ever<wbr>going<wbr>to<wbr>catch<wbr>me"!</p>

Any content inside wbr elements must not be considered part of the surrounding text.

4.6.28 Usage summary

This section is non-normative.

Element	Purpose	Example
`a`	Hyperlinks	Visit my <a href="drinks.html">drinks</a> page.
`em`	Stress emphasis	I must say I <em>adore</em> lemonade.
`strong`	Importance	This tea is <strong>very hot</strong>.
`small`	Side comments	These grapes are made into wine. <small>Alcohol is addictive.</small>
`s`	Inaccurate text	Price: <s>£4.50</s> £2.00!
`cite`	Titles of works	The case <cite>Hugo v. Danielle</cite> is relevant here.
`q`	Quotations	The judge said <q>You can drink water from the fish tank</q> but advised against it.
`dfn`	Defining instance	The term <dfn>organic food</dfn> refers to food produced without synthetic chemicals.
`abbr`	Abbreviations	Organic food in Ireland is certified by the <abbr title="Irish Organic Farmers and Growers Association">IOFGA</abbr>.
`time`	Date and/or time	Published <time>2009-10-21</time>.
`code`	Computer code	The <code>fruitdb</code> program can be used for tracking fruit production.
`var`	Variables	If there are <var>n</var> fruit in the bowl, at least <var>n</var>÷2 will be ripe.
`samp`	Computer output	The computer said <samp>Unknown error -3</samp>.
`kbd`	User input	Hit <kbd>F1</kbd> to continue.
`sub`	Subscripts	Water is H<sub>2</sub>O.
`sup`	Superscripts	The Hydrogen in heavy water is usually <sup>2</sup>H.
`i`	Alternative voice	Lemonade consists primarily of <i>Citrus limon</i>.
`b`	Keywords	Take a <b>lemon</b> and squeeze it with a <b>juicer</b>.
`u`	Annotations	The mixture of apple juice and <u class="spelling">eldeflower</u> juice is very pleasant.
`mark`	Highlight	Elderflower cordial, with one <mark>part</mark> cordial to ten <mark>part</mark>s water, stands a<mark>part</mark> from the rest.
`ruby`, `rt`, `rp`	Ruby annotations	<ruby> OJ <rp>(<rt>Orange Juice<rp>)</ruby>
`bdi`	Text directionality isolation	The recommended restaurant is <bdi lang="">My Juice Café (At The Beach)</bdi>.
`bdo`	Text directionality formatting	The proposal is to write English, but in reverse order. "Juice" would become "<bdo dir=rtl>Juice</bdo>"
`span`	Other	In French we call it <span lang="fr">sirop de sureau</span>.
`br`	Line break	Simply Orange Juice Company<br>Apopka, FL 32703<br>U.S.A.
`wbr`	Line breaking opportunity	www.simply<wbr>orange<wbr>juice.com

4.7 Edits

The ins and del elements represent edits to the document.

4.7.1 The `ins` element

Categories: Flow content.; When the element only contains phrasing content: phrasing content.
Contexts in which this element can be used:: When the element only contains phrasing content: where phrasing content is expected.; Otherwise: where flow content is expected.
Content model:: Transparent.
Content attributes:: Global attributes; cite; datetime
DOM interface:: Uses the HTMLModElement interface.

The ins element represents an addition to the document.

The following represents the addition of a single paragraph:

<aside>
 <ins>
  <p> I like fruit. </p>
 </ins>
</aside>

As does this, because everything in the aside element here counts as phrasing content and therefore there is just one paragraph:

<aside>
 <ins>
  Apples are <em>tasty</em>.
 </ins>
 <ins>
  So are pears.
 </ins>
</aside>

ins elements should not cross implied paragraph boundaries.

The following example represents the addition of two paragraphs, the second of which was inserted in two parts. The first ins element in this example thus crosses a paragraph boundary, which is considered poor form.

<aside>
 <!-- don't do this -->
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

Here is a better way of marking this up. It uses more elements, but none of the elements cross implied paragraph boundaries.

<aside>
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
 </ins>
 <ins datetime="2005-03-16T00:00Z">
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

4.7.2 The `del` element

Categories: Flow content.; When the element only contains phrasing content: phrasing content.
Contexts in which this element can be used:: When the element only contains phrasing content: where phrasing content is expected.; Otherwise: where flow content is expected.
Content model:: Transparent.
Content attributes:: Global attributes; cite; datetime
DOM interface:: Uses the HTMLModElement interface.

The del element represents a removal from the document.

del elements should not cross implied paragraph boundaries.

The following shows a "to do" list where items that have been done are crossed-off with the date and time of their completion.

<h1>To Do</h1>
<ul>
 <li>Empty the dishwasher</li>
 <li><del datetime="2009-10-11T01:25-07:00">Watch Walter Lewin's lectures</del></li>
 <li><del datetime="2009-10-10T23:38-07:00">Download more tracks</del></li>
 <li>Buy a printer</li>
</ul>

4.7.3 Attributes common to `ins` and `del` elements

The cite attribute may be used to specify the address of a document that explains the change. When that document is long, for instance the minutes of a meeting, authors are encouraged to include a fragment identifier pointing to the specific part of that document that discusses the change.

If the cite attribute is present, it must be a valid URL potentially surrounded by spaces that explains the change. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

The datetime attribute may be used to specify the time and date of the change.

If present, the datetime attribute's value must be a valid date string with optional time.

User agents must parse the datetime attribute according to the parse a date or time string algorithm. If that doesn't return a date or a global date and time, then the modification has no associated timestamp (the value is non-conforming; it is not a valid date string with optional time). Otherwise, the modification is marked as having been made at the given date or global date and time. If the given value is a global date and time then user agents should use the associated time-zone offset information to determine which time zone to present the given datetime in.

The ins and del elements must implement the HTMLModElement interface:

interface HTMLModElement : HTMLElement {
           attribute DOMString cite;
           attribute DOMString dateTime;
};

The cite IDL attribute must reflect the element's cite content attribute. The dateTime IDL attribute must reflect the element's datetime content attribute.

4.7.4 Edits and paragraphs

This section is non-normative.

Since the ins and del elements do not affect paragraphing, it is possible, in some cases where paragraphs are implied (without explicit p elements), for an ins or del element to span both an entire paragraph or other non-phrasing content elements and part of another paragraph. For example:

<section>
 <ins>
  <p>
   This is a paragraph that was inserted.
  </p>
  This is another paragraph whose first sentence was inserted
  at the same time as the paragraph above.
 </ins>
 This is a second sentence, which was there all along.
</section>

By only wrapping some paragraphs in p elements, one can even get the end of one paragraph, a whole second paragraph, and the start of a third paragraph to be covered by the same ins or del element (though this is very confusing, and not considered good practice):

<section>
 This is the first paragraph. <ins>This sentence was
 inserted.
 <p>This second paragraph was inserted.</p>
 This sentence was inserted too.</ins> This is the
 third paragraph in this example.
 <!-- (don't do this) -->
</section>

However, due to the way implied paragraphs are defined, it is not possible to mark up the end of one paragraph and the start of the very next one using the same ins or del element. You instead have to use one (or two) p element(s) and two ins or del elements, as for example:

<section>
 <p>This is the first paragraph. <del>This sentence was
 deleted.</del></p>
 <p><del>This sentence was deleted too.</del> That
 sentence needed a separate &lt;del&gt; element.</p>
</section>

Partly because of the confusion described above, authors are strongly encouraged to always mark up all paragraphs with the p element, instead of having ins or del elements that cross implied paragraphs boundaries.

4.7.5 Edits and lists

This section is non-normative.

The content models of the ol and ul elements do not allow ins and del elements as children. Lists always represent all their items, including items that would otherwise have been marked as deleted.

To indicate that an item is inserted or deleted, an ins or del element can be wrapped around the contents of the li element. To indicate that an item has been replaced by another, a single li element can have one or more del elements followed by one or more ins elements.

In the following example, a list that started empty had items added and removed from it over time. The bits in the example that have been emphasized show the parts that are the "current" state of the list. The list item numbers don't take into account the edits, though.

<h1>Stop-ship bugs</h1>
<ol>
 <li><ins datetime="2008-02-12T15:20Z">Bug 225:
 Rain detector doesn't work in snow</ins></li>
 <li><del datetime="2008-03-01T20:22Z"><ins datetime="2008-02-14T12:02Z">Bug 228:
 Water buffer overflows in April</ins></del></li>
 <li><ins datetime="2008-02-16T13:50Z">Bug 230:
 Water heater doesn't use renewable fuels</ins></li>
 <li><del datetime="2008-02-20T21:15Z"><ins datetime="2008-02-16T14:25Z">Bug 232:
 Carbon dioxide emissions detected after startup</ins></del></li>
</ol>

In the following example, a list that started with just fruit was replaced by a list with just colors.

<h1>List of <del>fruits</del><ins>colors</ins></h1>
<ul>
 <li><del>Lime</del><ins>Green</ins></li>
 <li><del>Apple</del></li>
 <li>Orange</li>
 <li><del>Pear</del></li>
 <li><ins>Teal</ins></li>
 <li><del>Lemon</del><ins>Yellow</ins></li>
 <li>Olive</li>
 <li><ins>Purple</ins></li>
</ul>

4.8 Embedded content

4.8.1 The `img` element

ISSUE-30 (longdesc) blocks progress to Last Call

Categories

If the element has a usemap attribute: Interactive content.

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

Empty.

Content attributes:

alt

src

usemap

ismap

width

height

DOM interface:

[NamedConstructor=Image(),
 NamedConstructor=Image(in unsigned long width),
 NamedConstructor=Image(in unsigned long width, in unsigned long height)]
interface HTMLImageElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString src;
           attribute DOMString useMap;
           attribute boolean isMap;
           attribute unsigned long width;
           attribute unsigned long height;
  readonly attribute unsigned long naturalWidth;
  readonly attribute unsigned long naturalHeight;
  readonly attribute boolean complete;
};

An img element represents an image.

The image given by the src attribute is the embedded content; the value of the alt attribute provides equivalent content for those who cannot process images or who have image loading disabled.

The src attribute must be present, and must contain a valid non-empty URL potentially surrounded by spaces referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted.

Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page vector documents (single-page PDFs, XML files with an SVG root element), animated bitmaps (APNGs, animated GIFs), animated vector graphics (XML files with an SVG root element that use declarative SMIL animation), and so forth. However, this also precludes SVG files with script, multipage PDF files, interactive MNG files, HTML documents, plain text documents, and so forth.

The requirements on the alt attribute's value are described in the next section.

The img element must not be used as a layout tool. In particular, img elements should not be used to display transparent images, as they rarely convey meaning and rarely add anything useful to the document.

An img is always in one of the following states:

Unavailable: The user agent hasn't obtained any image data.
Partially available: The user agent has obtained some of the image data.
Completely available: The user agent has obtained all of the image data.
Broken: The user agent has obtained all of the image data that it can, but it cannot decode the image (e.g. the image is corrupted, or the format is not supported, or no data could be obtained).

When an img element is either in the partially available state or in the completely available state, it is said to be available.

An img element is initially unavailable.

User agents may obtain images immediately or on demand.

A user agent that obtains images immediately must synchronously update the image data of an img element whenever that element is either created with a src attribute, or has its src attribute set, changed, or removed.

A user agent that obtains images on demand must update the image data of an img element whenever it needs the image data (i.e. on demand), but only if the img element has a src attribute, and if it has not updated the image data since the last time the src attribute was set. When an img element's src attribute is changed or removed, if the user agent only obtains images on demand, the img element must return to the unavailable state.

When the user agent is to update the image data of an img element, it must run the following steps:

Return the img element to the unavailable state.
If an instance of the fetching algorithm is still running for this element, then abort that algorithm, discarding any pending tasks generated by that algorithm.
Forget the img element's current image data, if any.
If the user agent cannot support images, or its support for images has been disabled, then abort these steps.
If the element's src attribute's value is the empty string, then set the element to the broken state, queue a task to fire a simple event named error at the img element, and abort these steps.
Otherwise, resolve the value of the element's src attribute, relative to the element, and, if that is successful, fetch that resource.

The resouce obtained in this fashion is the img element's image data.

Fetching the image must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.

This, unfortunately, can be used to perform a rudimentary port scan of the user's local network (especially in conjunction with scripting, though scripting isn't actually necessary to carry out such an attack). User agents may implement cross-origin access control policies that mitigate this attack, but unfortunately such policies are typically not compatible with existing Web content.

Each task that is queued by the networking task source while the image is being fetched must set the img element's state to partially available and update the presentation of the image appropriately.

The task that is queued by the networking task source once the resource has been fetched must act as appropriate given the following alternatives:

If the download was successful: Set the img element to the completely available state, update the presentation of the image appropriately, and queue a task to fire a simple event named load at the img element.
Otherwise: Set the img element to the broken state, and queue a task to fire a simple event named error at the img element.

If at any point the user agent discovers that the image data is corrupted in some fatal way, or that the image is not in a supported file format, then the user agent must set the img element to the broken state. If the fetching algorithm is still running for this element, then the user agent must also abort that algorithm, discarding any pending tasks generated by that algorithm, and then queue a task to fire a simple event named error at the img element.

When an img element is in the completely available state and the user agent can completely decode the media data without errors, then the img element is said to be fully decodable.

Whether the image is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the image's type and whether it is a valid image.

This allows servers to return images with error responses, and have them displayed.

The user agents should apply the image sniffing rules to determine the type of the image, with the image's associated Content-Type headers giving the official type. If these rules are not applied, then the type of the image must be the type given by the image's associated Content-Type headers.

User agents must not support non-image resources with the img element (e.g. XML files whose root element is an HTML element). User agents must not run executable code (e.g. scripts) embedded in the image resource. User agents must only display the first page of a multipage resource (e.g. a PDF file). User agents must not allow the resource to act in an interactive fashion, but should honor any animation in the resource.

This specification does not specify which image types are to be supported.

The task source for these tasks is the DOM manipulation task source.

What an img element represents depends on the src attribute and the alt attribute.

If the src attribute is set and the alt attribute is set to the empty string

The image is either decorative or supplemental to the rest of the content, redundant with some other information in the document.

If the image is available and the user agent is configured to display that image, then the element represents the element's image data.

Otherwise, the element represents nothing, and may be omitted completely from the rendering. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is set to a value that isn't empty

The image is a key part of the content; the alt attribute gives a textual equivalent or replacement for the image.

If the image is available and the user agent is configured to display that image, then the element represents the element's image data.

Otherwise, the element represents the text given by the alt attribute. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is not

The image might be a key part of the content, and there is no textual equivalent of the image available.

In a conforming document, the absence of the alt attribute indicates that the image is a key part of the content but that a textual replacement for the image was not available when the image was generated.

If the image is available and the user agent is configured to display that image, then the element represents the element's image data.

Otherwise, the user agent should display some sort of indicator that there is an image that is not being rendered, and may, if requested by the user, or if so configured, or when required to provide contextual information in response to navigation, provide caption information for the image, derived as follows:

If the image has a title attribute whose value is not the empty string, then the value of that attribute is the caption information; abort these steps.
If the image is a descendant of a figure element that has a child figcaption element, and, ignoring the figcaption element and its descendants, the figure element has no text node descendants other than inter-element whitespace, and no embedded content descendant other than the img element, then the contents of the first such figcaption element are the caption information; abort these steps.

If the src attribute is not set and either the alt attribute is set to the empty string or the alt attribute is not set at all

The element represents nothing.

Otherwise

The element represents the text given by the alt attribute.

The alt attribute does not represent advisory information. User agents must not present the contents of the alt attribute in the same way as content of the title attribute.

User agents may always provide the user with the option to display any image, or to prevent any image from being displayed.

While user agents are encouraged to repair cases of missing alt attributes, authors must not rely on such behavior. Requirements for providing text to act as an alternative for images are described in detail below.

The contents of img elements, if any, are ignored for the purposes of rendering.

The usemap attribute, if present, can indicate that the image has an associated image map.

The ismap attribute, when used on an element that is a descendant of an a element with an href attribute, indicates by its presence that the element provides access to a server-side image map. This affects how events are handled on the corresponding a element.

The ismap attribute is a boolean attribute. The attribute must not be specified on an element that does not have an ancestor a element with an href attribute.

The img element supports dimension attributes.

The IDL attributes alt, src, useMap, and isMap each must reflect the respective content attributes of the same name.

image . width [ = value ]

image . height [ = value ]

These attributes return the actual rendered dimensions of the image, or zero if the dimensions are not known.

They can be set, to change the corresponding content attributes.

image . naturalWidth

image . naturalHeight

These attributes return the intrinsic dimensions of the image, or zero if the dimensions are not known.

image . complete

Returns true if the image has been completely downloaded or if no image is specified; otherwise, returns false.

image = new Image( [ width [, height ] ] )

Returns a new img element, with the width and height attributes set to the values passed in the relevant arguments, if applicable.

The IDL attributes width and height must return the rendered width and height of the image, in CSS pixels, if the image is being rendered, and is being rendered to a visual medium; or else the intrinsic width and height of the image, in CSS pixels, if the image is available but not being rendered to a visual medium; or else 0, if the image is not available. [CSS]

On setting, they must act as if they reflected the respective content attributes of the same name.

The IDL attributes naturalWidth and naturalHeight must return the intrinsic width and height of the image, in CSS pixels, if the image is available, or else 0. [CSS]

The IDL attribute complete must return true if any of the following conditions is true:

The src attribute is omitted.
The src attribute's value is the empty string.
The final task that is queued by the networking task source once the resource has been fetched has been queued, but has not yet been run, and the img element is not in the broken state.
The img element is completely available.

Otherwise, the attribute must return false.

The value of complete can thus change while a script is executing.

Three constructors are provided for creating HTMLImageElement objects (in addition to the factory methods from DOM Core such as createElement()): Image(), Image(width), and Image(width, height). When invoked as constructors, these must return a new HTMLImageElement object (a new img element). If the width argument is present, the new object's width content attribute must be set to width. If the height argument is also present, the new object's height content attribute must be set to height. The element's document must be the active document of the browsing context of the Window object on which the interface object of the invoked constructor is found.

A single image can have different appropriate alternative text depending on the context.

In each of the following cases, the same image is used, yet the alt text is different each time. The image is the coat of arms of the Carouge municipality in the canton Geneva in Switzerland.

Here it is used as a supplementary icon:

<p>I lived in <img src="carouge.svg" alt=""> Carouge.</p>

Here it is used as an icon representing the town:

<p>Home town: <img src="carouge.svg" alt="Carouge"></p>

Here it is used as part of a text on the town:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt="The coat of arms depicts a lion, sitting in front of a tree."></p>
<p>It is used as decoration all over the town.</p>

Here it is used as a way to support a similar text where the description is given as well as, instead of as an alternative to, the image:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt=""></p>
<p>The coat of arms depicts a lion, sitting in front of a tree.
It is used as decoration all over the town.</p>

Here it is used as part of a story:

<p>He picked up the folder and a piece of paper fell out.</p>
<p><img src="carouge.svg" alt="Shaped like a shield, the paper had a
red background, a green tree, and a yellow lion with its tongue
hanging out and whose tail was shaped like an S."></p>
<p>He stared at the folder. S! The answer he had been looking for all
this time was simply the letter S! How had he not seen that before? It all
came together now. The phone call where Hector had referred to a lion's tail,
the time Marco had stuck his tongue out...</p>

Here it is not known at the time of publication what the image will be, only that it will be a coat of arms of some kind, and thus no replacement text can be provided, and instead only a brief caption for the image is provided, in the title attribute:

<p>The last user to have uploaded a coat of arms uploaded this one:</p>
<p><img src="last-uploaded-coat-of-arms.cgi" title="User-uploaded coat of arms."></p>

Ideally, the author would find a way to provide real replacement text even in this case, e.g. by asking the previous user. Not providing replacement text makes the document more difficult to use for people who are unable to view images, e.g. blind users, or users or very low-bandwidth connections or who pay by the byte, or users who are forced to use a text-only Web browser.

Here are some more examples showing the same picture used in different contexts, with different appropriate alternate texts each time.

<article>
 <h1>My cats</h1>
 <h2>Fluffy</h2>
 <p>Fluffy is my favorite.</p>
 <img src="fluffy.jpg" alt="She likes playing with a ball of yarn.">
 <p>She's just too cute.</p>
 <h2>Miles</h2>
 <p>My other cat, Miles just eats and sleeps.</p>
</article>

<article>
 <h1>Photography</h1>
 <h2>Shooting moving targets indoors</h2>
 <p>The trick here is to know how to anticipate; to know at what speed and
 what distance the subject will pass by.</p>
 <img src="fluffy.jpg" alt="A cat flying by, chasing a ball of yarn, can be
 photographed quite nicely using this technique.">
 <h2>Nature by night</h2>
 <p>To achieve this, you'll need either an extremely sensitive film, or
 immense flash lights.</p>
</article>

<article>
 <h1>About me</h1>
 <h2>My pets</h2>
 <p>I've got a cat named Fluffy and a dog named Miles.</p>
 <img src="fluffy.jpg" alt="Fluffy, my cat, tends to keep itself busy.">
 <p>My dog Miles and I like go on long walks together.</p>
 <h2>music</h2>
 <p>After our walks, having emptied my mind, I like listening to Bach.</p>
</article>

<article>
 <h1>Fluffy and the Yarn</h1>
 <p>Fluffy was a cat who liked to play with yarn. He also liked to jump.</p>
 <aside><img src="fluffy.jpg" alt="" title="Fluffy"></aside>
 <p>He would play in the morning, he would play in the evening.</p>
</article>

4.8.1.1 Requirements for providing text to act as an alternative for images

4.8.1.1.1 General guidelines

Except where otherwise specified, the alt attribute must be specified and its value must not be empty; the value must be an appropriate replacement for the image. The specific requirements for the alt attribute depend on what the image is intended to represent, as described in the following sections.

The most general rule to consider when writing alternative text is the following: the intent is that replacing every image with the text of its alt attribute not change the meaning of the page.

So, in general, alternative text can be written by considering what one would have written had one not been able to include the image.

A corollary to this is that the alt attribute's value should never contain text that could be considered the image's caption, title, or legend. It is supposed to contain replacement text that could be used by users instead of the image; it is not meant to supplement the image. The title attribute can be used for supplemental information.

One way to think of alternative text is to think about how you would read the page containing the image to someone over the phone, without mentioning that there is an image present. Whatever you say instead of the image is typically a good start for writing the alternative text.

4.8.1.1.2 A link or button containing nothing but the image

When an a element that creates a hyperlink, or a button element, has no textual content but contains one or more images, the alt attributes must contain text that together convey the purpose of the link or button.

In this example, a user is asked to pick his preferred color from a list of three. Each color is given by an image, but for users who have configured their user agent not to display images, the color names are used instead:

<h1>Pick your color</h1>
<ul>
 <li><a href="green.html"><img src="green.jpeg" alt="Green"></a></li>
 <li><a href="blue.html"><img src="blue.jpeg" alt="Blue"></a></li>
 <li><a href="red.html"><img src="red.jpeg" alt="Red"></a></li>
</ul>

In this example, each button has a set of images to indicate the kind of color output desired by the user. The first image is used in each case to give the alternative text.

<button name="rgb"><img src="red" alt="RGB"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>

Since each image represents one part of the text, it could also be written like this:

<button name="rgb"><img src="red" alt="R"><img src="green" alt="G"><img src="blue" alt="B"></button>
<button name="cmyk"><img src="cyan" alt="C"><img src="magenta" alt="M"><img src="yellow" alt="Y"><img src="black" alt="K"></button>

However, with other alternative text, this might not work, and putting all the alternative text into one image in each case might make more sense:

<button name="rgb"><img src="red" alt="sRGB profile"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK profile"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>

4.8.1.1.3 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations

Sometimes something can be more clearly stated in graphical form, for example as a flowchart, a diagram, a graph, or a simple map showing directions. In such cases, an image can be given using the img element, but the lesser textual version must still be given, so that users who are unable to view the image (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind) are still able to understand the message being conveyed.

The text must be given in the alt attribute, and must convey the same message as the image specified in the src attribute.

It is important to realize that the alternative text is a replacement for the image, not a description of the image.

In the following example we have a flowchart in image form, with text in the alt attribute rephrasing the flowchart in prose form:

<p>In the common case, the data handled by the tokenization stage
comes from the network, but it can also come from script.</p>
<p><img src="http://dev.w3.org/html5/spec/images/parsing-model-overview.png" alt="The network
passes data to the Tokenizer stage, which passes data to the Tree
Construction stage. From there, data goes to both the DOM and to
Script Execution. Script Execution is linked to the DOM, and, using
document.write(), passes data to the Tokenizer."></p>

Here's another example, showing a good solution and a bad solution to the problem of including an image in a description.

First, here's the good solution. This sample shows how the alternative text should just be what you would have put in the prose if the image had never existed.

<!-- This is the correct way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="The house is white, with a boarded front door.">
 There is a small mailbox here.
</p>

Second, here's the bad solution. In this incorrect way of doing things, the alternative text is simply a description of the image, instead of a textual replacement for the image. It's bad because when the image isn't shown, the text doesn't flow as well as in the first example.

<!-- This is the wrong way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="A white house, with a boarded front door.">
 There is a small mailbox here.
</p>

Text such as "Photo of white house with boarded door" would be equally bad alternative text (though it could be suitable for the title attribute or in the figcaption element of a figure with this image).

4.8.1.1.4 A short phrase or label with an alternative graphical representation: icons, logos

A document can contain information in iconic form. The icon is intended to help users of visual browsers to recognize features at a glance.

In some cases, the icon is supplemental to a text label conveying the same meaning. In those cases, the alt attribute must be present but must be empty.

Here the icons are next to text that conveys the same meaning, so they have an empty alt attribute:

<nav>
 <p><a href="/help/"><img src="/icons/help.png" alt=""> Help</a></p>
 <p><a href="/configure/"><img src="/icons/configuration.png" alt="">
 Configuration Tools</a></p>
</nav>

In other cases, the icon has no text next to it describing what it means; the icon is supposed to be self-explanatory. In those cases, an equivalent textual label must be given in the alt attribute.

Here, posts on a news site are labeled with an icon indicating their topic.

<body>
 <article>
  <header>
   <h1>Ratatouille wins <i>Best Movie of the Year</i> award</h1>
   <p><img src="movies.png" alt="Movies"></p>
  </header>
  <p>Pixar has won yet another <i>Best Movie of the Year</i> award,
  making this its 8th win in the last 12 years.</p>
 </article>
 <article>
  <header>
   <h1>Latest TWiT episode is online</h1>
   <p><img src="podcasts.png" alt="Podcasts"></p>
  </header>
  <p>The latest TWiT episode has been posted, in which we hear
  several tech news stories as well as learning much more about the
  iPhone. This week, the panelists compare how reflective their
  iPhones' Apple logos are.</p>
 </article>
</body>

Many pages include logos, insignia, flags, or emblems, which stand for a particular entity such as a company, organization, project, band, software package, country, or some such.

If the logo is being used to represent the entity, e.g. as a page heading, the alt attribute must contain the name of the entity being represented by the logo. The alt attribute must not contain text like the word "logo", as it is not the fact that it is a logo that is being conveyed, it's the entity itself.

If the logo is being used next to the name of the entity that it represents, then the logo is supplemental, and its alt attribute must instead be empty.

If the logo is merely used as decorative material (as branding, or, for example, as a side image in an article that mentions the entity to which the logo belongs), then the entry below on purely decorative images applies. If the logo is actually being discussed, then it is being used as a phrase or paragraph (the description of the logo) with an alternative graphical representation (the logo itself), and the first entry above applies.

In the following snippets, all four of the above cases are present. First, we see a logo used to represent a company:

<h1><img src="XYZ.gif" alt="The XYZ company"></h1>

Next, we see a paragraph which uses a logo right next to the company name, and so doesn't have any alternative text:

<article>
 <h2>News</h2>
 <p>We have recently been looking at buying the <img src="alpha.gif"
 alt=""> ΑΒΓ company, a small Greek company
 specializing in our type of product.</p>

In this third snippet, we have a logo being used in an aside, as part of the larger article discussing the acquisition:

 <aside><p><img src="alpha-large.gif" alt=""></p></aside>
 <p>The ΑΒΓ company has had a good quarter, and our
 pie chart studies of their accounts suggest a much bigger blue slice
 than its green and orange slices, which is always a good sign.</p>
</article>

Finally, we have an opinion piece talking about a logo, and the logo is therefore described in detail in the alternative text.

<p>Consider for a moment their logo:</p>

<p><img src="/images/logo" alt="It consists of a green circle with a
green question mark centered inside it."></p>

<p>How unoriginal can you get? I mean, oooooh, a question mark, how
<em>revolutionary</em>, how utterly <em>ground-breaking</em>, I'm
sure everyone will rush to adopt those specifications now! They could
at least have tried for some sort of, I don't know, sequence of
rounded squares with varying shades of green and bold white outlines,
at least that would look good on the cover of a blue book.</p>

This example shows how the alternative text should be written such that if the image isn't available, and the text is used instead, the text flows seamlessly into the surrounding text, as if the image had never been there in the first place.

4.8.1.1.5 Text that has been rendered to a graphic for typographical effect

Sometimes, an image just consists of text, and the purpose of the image is not to highlight the actual typographic effects used to render the text, but just to convey the text itself.

In such cases, the alt attribute must be present but must consist of the same text as written in the image itself.

Consider a graphic containing the text "Earth Day", but with the letters all decorated with flowers and plants. If the text is merely being used as a heading, to spice up the page for graphical users, then the correct alternative text is just the same text "Earth Day", and no mention need be made of the decorations:

<h1><img src="earthdayheading.png" alt="Earth Day"></h1>

4.8.1.1.6 A graphical representation of some of the surrounding text

In many cases, the image is actually just supplementary, and its presence merely reinforces the surrounding text. In these cases, the alt attribute must be present but its value must be the empty string.

In general, an image falls into this category if removing the image doesn't make the page any less useful, but including the image makes it a lot easier for users of visual browsers to understand the concept.

A flowchart that repeats the previous paragraph in graphical form:

<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="http://dev.w3.org/html5/spec/images/parsing-model-overview.png" alt=""></p>

In these cases, it would be wrong to include alternative text that consists of just a caption. If a caption is to be included, then either the title attribute can be used, or the figure and figcaption elements can be used. In the latter case, the image would in fact be a phrase or paragraph with an alternative graphical representation, and would thus require alternative text.

<!-- Using the title="" attribute -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="http://dev.w3.org/html5/spec/images/parsing-model-overview.png" alt=""
        title="Flowchart representation of the parsing model."></p>

<!-- Using <figure> and <figcaption> -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<figure>
 <img src="http://dev.w3.org/html5/spec/images/parsing-model-overview.png" alt="The Network leads
 to the Tokenizer, which leads to the Tree Construction. The Tree
 Construction leads to two items. The first is Script Execution, which
 leads via document.write() back to the Tokenizer. The second item
 from which Tree Construction leads is the DOM. The DOM is related to
 the Script Execution.">
 <figcaption>Flowchart representation of the parsing model.</figcaption>
</figure>

<!-- This is WRONG. Do not do this. Instead, do what the above examples do. -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="http://dev.w3.org/html5/spec/images/parsing-model-overview.png"
        alt="Flowchart representation of the parsing model."></p>
<!-- Never put the image's caption in the alt="" attribute! -->

A graph that repeats the previous paragraph in graphical form:

<p>According to a study covering several billion pages,
about 62% of documents on the Web in 2007 triggered the Quirks
rendering mode of Web browsers, about 30% triggered the Almost
Standards mode, and about 9% triggered the Standards mode.</p>
<p><img src="rendering-mode-pie-chart.png" alt=""></p>

4.8.1.1.7 A purely decorative image that doesn't add any information

If an image is decorative but isn't especially page-specific — for example an image that forms part of a site-wide design scheme — the image should be specified in the site's CSS, not in the markup of the document.

Exceptions to this rule, in cases where CSS cannot be used to display an entirely decorative image, are covered by the HTML5: Techniques for providing useful text alternatives. [HTMLALTTECHS] Authors are also encouraged to consult the Web Content Accessibility Guidelines 2.0 for more detailed information and acceptable techniques. [WCAG]

4.8.1.1.8 A group of images that form a single larger picture with no links

When a picture has been sliced into smaller image files that are then displayed together to form the complete picture again, one of the images must have its alt attribute set as per the relevant rules that would be appropriate for the picture as a whole, and then all the remaining images must have their alt attribute set to the empty string.

In the following example, a picture representing a company logo for XYZ Corp has been split into two pieces, the first containing the letters "XYZ" and the second with the word "Corp". The alternative text ("XYZ Corp") is all in the first image.

<h1><img src="logo1.png" alt="XYZ Corp"><img src="logo2.png" alt=""></h1>

In the following example, a rating is shown as three filled stars and two empty stars. While the alternative text could have been "★★★☆☆", the author has instead decided to more helpfully give the rating in the form "3 out of 5". That is the alternative text of the first image, and the rest have blank alternative text.

<p>Rating: <meter max=5 value=3><img src="1" alt="3 out of 5"
  ><img src="1" alt=""><img src="1" alt=""><img src="0" alt=""
  ><img src="0" alt=""></meter></p>

4.8.1.1.9 A group of images that form a single larger picture with links

Generally, image maps should be used instead of slicing an image for links.

However, if an image is indeed sliced and any of the components of the sliced picture are the sole contents of links, then one image per link must have alternative text in its alt attribute representing the purpose of the link.

In the following example, a picture representing the flying spaghetti monster emblem, with each of the left noodly appendages and the right noodly appendages in different images, so that the user can pick the left side or the right side in an adventure.

<h1>The Church</h1>
<p>You come across a flying spaghetti monster. Which side of His
Noodliness do you wish to reach out for?</p>
<p><a href="?go=left" ><img src="fsm-left.png"  alt="Left side. "></a
  ><img src="fsm-middle.png" alt=""
  ><a href="?go=right"><img src="fsm-right.png" alt="Right side."></a></p>

4.8.1.1.10 A key part of the content

In some cases, the image is a critical part of the content. This could be the case, for instance, on a page that is part of a photo gallery. The image is the whole point of the page containing it.

How to provide alternative text for an image that is a key part of the content depends on the image's provenance.

The general case

When it is possible for detailed alternative text to be provided, for example if the image is part of a series of screenshots in a magazine review, or part of a comic strip, or is a photograph in a blog entry about that photograph, text that can serve as a substitute for the image must be given as the contents of the alt attribute.

A screenshot in a gallery of screenshots for a new OS, with some alternative text:

<figure>
 <img src="KDE%20Light%20desktop.png"
      alt="The desktop is blue, with icons along the left hand side in
           two columns, reading System, Home, K-Mail, etc. A window is
           open showing that menus wrap to a second line if they
           cannot fit in the window. The window has a list of icons
           along the top, with an address bar below it, a list of
           icons for tabs along the left edge, a status bar on the
           bottom, and two panes in the middle. The desktop has a bar
           at the bottom of the screen with a few buttons, a pager, a
           list of open applications, and a clock.">
 <figcaption>Screenshot of a KDE desktop.</figcaption>
</figure>

A graph in a financial report:

<img src="sales.gif"
     title="Sales graph"
     alt="From 1998 to 2005, sales increased by the following percentages
     with each year: 624%, 75%, 138%, 40%, 35%, 9%, 21%">

Note that "sales graph" would be inadequate alternative text for a sales graph. Text that would be a good caption is not generally suitable as replacement text.

Images that defy a complete description

In certain cases, the nature of the image might be such that providing thorough alternative text is impractical. For example, the image could be indistinct, or could be a complex fractal, or could be a detailed topographical map.

In these cases, the alt attribute must contain some suitable alternative text, but it may be somewhat brief.

Sometimes there simply is no text that can do justice to an image. For example, there is little that can be said to usefully describe a Rorschach inkblot test. However, a description, even if brief, is still better than nothing:

<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A shape with left-right
 symmetry with indistinct edges, with a small gap in the center, two
 larger gaps offset slightly from the center, with two similar gaps
 under them. The outline is wider in the top half than the bottom
 half, with the sides extending upwards higher than the center, and
 the center extending below the sides.">
 <figcaption>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</figcaption>
</figure>

Note that the following would be a very bad use of alternative text:

<!-- This example is wrong. Do not copy it. -->
<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A black outline
 of the first of the ten cards in the Rorschach inkblot test.">
 <figcaption>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</figcaption>
</figure>

Including the caption in the alternative text like this isn't useful because it effectively duplicates the caption for users who don't have images, taunting them twice yet not helping them any more than if they had only read or heard the caption once.

Another example of an image that defies full description is a fractal, which, by definition, is infinite in detail.

The following example shows one possible way of providing alternative text for the full view of an image of the Mandelbrot set.

<img src="ms1.jpeg" alt="The Mandelbrot set appears as a cardioid with
its cusp on the real axis in the positive direction, with a smaller
bulb aligned along the same center line, touching it in the negative
direction, and with these two shapes being surrounded by smaller bulbs
of various sizes.">

Images whose contents are not known

In some unfortunate cases, there might be no alternative text available at all, either because the image is obtained in some automated fashion without any associated alternative text (e.g. a Webcam), or because the page is being generated by a script using user-provided images where the user did not provide suitable or usable alternative text (e.g. photograph sharing sites), or because the author does not himself know what the images represent (e.g. a blind photographer sharing an image on his blog).

In such cases, the alt attribute may be omitted, but one of the following conditions must be met as well:

The title attribute is present and has a non-empty value.
The img element is in a figure element that contains a figcaption element that contains content other than inter-element whitespace, and, ignoring the figcaption element and its descendants, the figure element has no text node descendants other than inter-element whitespace, and no embedded content descendant other than the img element.

Such cases are to be kept to an absolute minimum. If there is even the slightest possibility of the author having the ability to provide real alternative text, then it would not be acceptable to omit the alt attribute.

A photo on a photo-sharing site, if the site received the image with no metadata other than the caption, could be marked up as follows:

<figure>
 <img src="1100670787_6a7c664aef.jpg">
 <figcaption>Bubbles traveled everywhere with us.</figcaption>
</figure>

It would be better, however, if a detailed description of the important parts of the image obtained from the user and included on the page.

A blind user's blog in which a photo taken by the user is shown. Initially, the user might not have any idea what the photo he took shows:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg">
  <figcaption>A photograph taken blindly from my front porch.</figcaption>
 </figure>
</article>

Eventually though, the user might obtain a description of the image from his friends and could then include alternative text:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg" alt="The photograph shows my hummingbird
  feeder hanging from the edge of my roof. It is half full, but there
  are no birds around. In the background, out-of-focus trees fill the
  shot. The feeder is made of wood with a metal grate, and it contains
  peanuts. The edge of the roof is wooden too, and is painted white
  with light blue streaks.">
  <figcaption>A photograph taken blindly from my front porch.</figcaption>
 </figure>
</article>

Sometimes the entire point of the image is that a textual description is not available, and the user is to provide the description. For instance, the point of a CAPTCHA image is to see if the user can literally read the graphic. Here is one way to mark up a CAPTCHA (note the title attribute):

<p><label>What does this image say?
<img src="captcha.cgi?id=8934" title="CAPTCHA">
<input type=text name=captcha></label>
(If you cannot see the image, you can use an <a
href="?audio">audio</a> test instead.)</p>

Another example would be software that displays images and asks for alternative text precisely for the purpose of then writing a page with correct alternative text. Such a page could have a table of images, like this:

<table>
 <thead>
  <tr> <th> Image <th> Description
 <tbody>
  <tr>
   <td> <img src="2421.png" title="Image 640 by 100, filename 'banner.gif'">
   <td> <input name="alt2421">
  <tr>
   <td> <img src="2422.png" title="Image 200 by 480, filename 'ad3.gif'">
   <td> <input name="alt2422">
</table>

Notice that even in this example, as much useful information as possible is still included in the title attribute.

Since some users cannot use images at all (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind), the alt attribute is only allowed to be omitted rather than being provided with replacement text when no alternative text is available and none can be made available, as in the above examples. Lack of effort from the part of the author is not an acceptable reason for omitting the alt attribute.

4.8.1.1.11 An image not intended for the user

Generally authors should avoid using img elements for purposes other than showing images.

If an img element is being used for purposes other than showing an image, e.g. as part of a service to count page views, then the alt attribute must be the empty string.

In such cases, the width and height attributes should both be set to zero.

4.8.1.1.12 Guidance for markup generators

Markup generators (such as WYSIWYG authoring tools) should, wherever possible, obtain alternative text from their users. However, it is recognized that in many cases, this will not be possible.

For images that are the sole contents of links, markup generators should examine the link target to determine the title of the target, or the URL of the target, and use information obtained in this manner as the alternative text.

As a last resort, implementors should either set the alt attribute to the empty string, under the assumption that the image is a purely decorative image that doesn't add any information but is still specific to the surrounding content, or omit the alt attribute altogether, under the assumption that the image is a key part of the content.

Markup generators should generally avoid using the image's own file name as the alternative text. Similarly, markup generators should avoid generating alternative text from any content that will be equally available to presentation user agents (e.g. Web browsers).

This is because once a page is generated, it will typically not be updated, whereas the browsers that later read the page can be updated by the user, therefore the browser is likely to have more up-to-date and finely-tuned heuristics than the markup generator did when generating the page.

4.8.1.1.13 Guidance for conformance checkers

A conformance checker must report the lack of an alt attribute as an error unless one of the conditions listed below applies:

The title attribute is present and has a non-empty value (as described above).
The img element is in a figure element that satisfies the conditions described above.
The document has a meta element with a name attribute whose value is an ASCII case-insensitive match for the string "generator". (This case does not represent a case where the document is conforming, only that the generator could not determine appropriate alternative text — validators are required to not show an error in this case to discourage markup generators from including bogus alternative text purely in an attempt to silence validators.)

4.8.2 The `iframe` element

Categories

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

Text that conforms to the requirements given in the prose.

Content attributes:

src

srcdoc

name

sandbox

seamless

width

height

DOM interface:

interface HTMLIFrameElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString srcdoc;
           attribute DOMString name;
  [PutForwards=value] readonly attribute DOMSettableTokenList sandbox;
           attribute boolean seamless;
           attribute DOMString width;
           attribute DOMString height;
  readonly attribute Document contentDocument;
  readonly attribute WindowProxy contentWindow;
};

The iframe element represents a nested browsing context.

The src attribute gives the address of a page that the nested browsing context is to contain. The attribute, if present, must be a valid non-empty URL potentially surrounded by spaces.

The srcdoc attribute gives the content of the page that the nested browsing context is to contain. The value of the attribute is the source of an iframe srcdoc document.

For iframe elements in HTML documents, the attribute, if present, must have a value using the HTML syntax that consists of the following syntactic components, in the given order:

Any number of comments and space characters.
Optionally, a DOCTYPE.
Any number of comments and space characters.
The root element, in the form of an html element.
Any number of comments and space characters.

For iframe elements in XML documents, the attribute, if present, must have a value that matches the production labeled document in the XML specification. [XML]

If the src attribute and the srcdoc attribute are both specified together, the srcdoc attribute takes priority. This allows authors to provide a fallback URL for legacy user agents that do not support the srcdoc attribute.

When an iframe element is first inserted into a document, the user agent must create a nested browsing context, and then process the iframe attributes for the first time.

Whenever an iframe element with a nested browsing context has its srcdoc attribute set, changed, or removed, the user agent must process the iframe attributes.

Similarly, whenever an iframe element with a nested browsing context but with no srcdoc attribute specified has its src attribute set, changed, or removed, the user agent must process the iframe attributes.

When the user agent is to process the iframe attributes, it must run the first appropriate steps from the following list:

If the srcdoc attribute is specified

Navigate the element's browsing context to a resource whose Content-Type is text/html, whose URL is about:srcdoc, and whose data consists of the value of the attribute. The resulting Document must be considered an iframe srcdoc document.

If the src attribute is specified but the srcdoc attribute is not

If the value of the src attribute is the empty string, jump to the empty step below.
Resolve the value of the src attribute, relative to the iframe element.
If that is not successful, then jump to the empty step below.
If the resulting absolute URL is an ASCII case-insensitive match for the string "about:blank", and the user agent is processing this iframe's attributes for the first time, then jump to the empty step below. (In cases other than the first time, about:blank is loaded normally.)
Navigate the element's browsing context to the resulting absolute URL.

Empty: When the steps above require the user agent to jump to the empty step, if the user agent is processing this iframe's attributes for the first time, then the user agent must queue a task to fire a simple event named load at the iframe element. (After jumping to this step, the above steps are not resumed.)

Otherwise

Queue a task to fire a simple event named load at the iframe element.

Any navigation required of the user agent in the process the iframe attributes algorithm must be completed with the iframe element's document's browsing context as the source browsing context.

Furthermore, if the browsing context's session history contained only one Document when the process the iframe attributes algorithm was invoked, and that was the about:blank Document created when the browsing context was created, then any navigation required of the user agent in that algorithm must be completed with replacement enabled.

If, when the element is created, the srcdoc attribute is not set, and the src attribute is either also not set or set but its value cannot be resolved, the browsing context will remain at the initial about:blank page.

If the user navigates away from this page, the iframe's corresponding WindowProxy object will proxy new Window objects for new Document objects, but the src attribute will not change.

Removing an iframe from a Document does not cause its browsing context to be discarded. Indeed, an iframe's browsing context can survive its original parent Document if its iframe is moved to another Document.

On the other hand, if an iframe is removed from a Document and is then subsequently garbage collected, this will likely mean (in the absence of other references) that the child browsing context's WindowProxy object will become eligble for garbage collection, which will then lead to that browsing context being discarded, which will then lead to its Document being discarded also. This happens without notice to any scripts running in that Document; for example, no unload events are fired (the "unload a document" steps are not run).

Here a blog uses the srcdoc attribute in conjunction with the sandbox and seamless attributes described below to provide users of user agents that support this feature with an extra layer of protection from script injection in the blog post comments:

<article>
 <h1>I got my own magazine!</h1>
 <p>After much effort, I've finally found a publisher, and so now I
 have my own magazine! Isn't that awesome?! The first issue will come
 out in September, and we have articles about getting food, and about
 getting in boxes, it's going to be great!</p>
 <footer>
  <p>Written by <a href="/users/cap">cap</a>.
  <time pubdate>2009-08-21T23:32Z</time></p>
 </footer>
 <article>
  <footer> At <time pubdate>2009-08-21T23:35Z</time>, <a href="/users/ch">ch</a> writes: </footer>
  <iframe seamless sandbox srcdoc="<p>did you get a cover picture yet?"></iframe>
 </article>
 <article>
  <footer> At <time pubdate>2009-08-21T23:44Z</time>, <a href="/users/cap">cap</a> writes: </footer>
  <iframe seamless sandbox srcdoc="<p>Yeah, you can see it <a href=&quot;/gallery?mode=cover&amp;amp;page=1&quot;>in my gallery</a>."></iframe>
 </article>
 <article>
  <footer> At <time pubdate>2009-08-21T23:58Z</time>, <a href="/users/ch">ch</a> writes: </footer>
  <iframe seamless sandbox srcdoc="<p>hey that's earl's table.
<p>you should get earl&amp;amp;me on the next cover."></iframe>
 </article>

Notice the way that quotes have to be escaped (otherwise the sandbox attribute would end prematurely), and the way raw ampersands (e.g. in URLs or in prose) mentioned in the sandboxed content have to be doubly escaped — once so that the ampersand is preserved when originally parsing the sandbox attribute, and once more to prevent the ampersand from being misinterpreted when parsing the sandboxed content.

In the HTML syntax, authors need only remember to use U+0022 QUOTATION MARK characters (") to wrap the attribute contents and then to escape all U+0022 QUOTATION MARK (") and U+0026 AMPERSAND (&) characters, and to specify the sandbox attribute, to ensure safe embedding of content.

Due to restrictions of the XML syntax, in XML the U+003C LESS-THAN SIGN character (<) needs to be escaped as well. In order to prevent attribute-value normalization, some of XML's whitespace characters — specifically U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) — also need to be escaped. [XML]

The name attribute, if present, must be a valid browsing context name. The given value is used to name the nested browsing context. When the browsing context is created, if the attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

Whenever the name attribute is set, the nested browsing context's name must be changed to the new value. If the attribute is removed, the browsing context name must be set to the empty string.

When content loads in an iframe, after any load events are fired within the content itself, the user agent must queue a task to fire a simple event named load at the iframe element. When content whose URL has the same origin as the iframe element's Document fails to load (e.g. due to a DNS error, network error, or if the server returned a 4xx or 5xx status code or equivalent), then the user agent must queue a task to fire a simple event named error at the element instead. (This event does not fire for parse errors, script errors, or any errors for cross-origin resources.)

The task source for these tasks is the DOM manipulation task source.

A load event is also fired at the iframe element when it is created if no other data is loaded in it.

When there is an active parser in the iframe, and when anything in the iframe is delaying the load event of the iframe's browsing context's active document, the iframe must delay the load event of its document.

If, during the handling of the load event, the browsing context in the iframe is again navigated, that will further delay the load event.

The sandbox attribute, when specified, enables a set of extra restrictions on any content hosted by the iframe. Its value must be an unordered set of unique space-separated tokens that are ASCII case-insensitive. The allowed values are allow-same-origin, allow-top-navigation, allow-forms, and allow-scripts. When the attribute is set, the content is treated as being from a unique origin, forms and scripts are disabled, links are prevented from targeting other browsing contexts, and plugins are disabled. The allow-same-origin keyword allows the content to be treated as being from the same origin instead of forcing it into a unique origin, the allow-top-navigation keyword allows the content to navigate its top-level browsing context, and the allow-forms and allow-scripts keywords re-enable forms and scripts respectively (though scripts are still prevented from creating popups).

Setting both the allow-scripts and allow-same-origin keywords together when the embedded page has the same origin as the page containing the iframe allows the embedded page to simply remove the sandbox attribute.

Sandboxing hostile content is of minimal help if an attacker can convince the user to just visit the hostile content directly, rather than in the iframe. To limit the damage that can be caused by hostile HTML content, it should be served using the text/html-sandboxed MIME type.

While the sandbox attribute is specified, the iframe element's nested browsing context must have the flags given in the following list set. In addition, any browsing contexts nested within an iframe, either directly or indirectly, must have all the flags set on them as were set on the iframe's Document's browsing context when the iframe's Document was created.

The sandboxed navigation browsing context flag

This flag prevents content from navigating browsing contexts other than the sandboxed browsing context itself (or browsing contexts further nested inside it), and the top-level browsing context (which is protected by the sandboxed top-level navigation browsing context flag defined next).

This flag also prevents content from creating new auxiliary browsing contexts, e.g. using the target attribute or the window.open() method.

The sandboxed top-level navigation browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-top-navigation keyword set

This flag prevents content from navigating their top-level browsing context.

When the allow-top-navigation is set, content can navigate its top-level browsing context, but other browsing contexts are still protected by the sandboxed navigation browsing context flag defined above.

The sandboxed plugins browsing context flag

This flag prevents content from instantiating plugins, whether using the embed element, the object element, the applet element, or through navigation of a nested browsing context.

The sandboxed seamless iframes flag

This flag prevents content from using the seamless attribute on descendant iframe elements.

This prevents a page inserted using the allow-same-origin keyword from using a CSS-selector-based method of probing the DOM of other pages on the same site (in particular, pages that contain user-sensitive information).

The sandboxed origin browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-same-origin keyword set

This flag forces content into a unique origin, thus preventing it from accessing other content from the same origin.

This flag also prevents script from reading from or writing to the document.cookie IDL attribute, and blocks access to localStorage. [WEBSTORAGE]

The allow-same-origin attribute is intended for two cases.

First, it can be used to allow content from the same site to be sandboxed to disable scripting, while still allowing access to the DOM of the sandboxed content.

Second, it can be used to embed content from a third-party site, sandboxed to prevent that site from opening popup windows, etc, without preventing the embedded page from communicating back to its originating site, using the database APIs to store data, etc.

The sandboxed forms browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-forms keyword set

This flag blocks form submission.

The sandboxed scripts browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-scripts keyword set

This flag blocks script execution.

The sandboxed automatic features browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-scripts keyword (defined above) set

This flag blocks features that trigger automatically, such as automatically playing a video or automatically focusing a form control. It is relaxed by the same flag as scripts, because when scripts are enabled these features are trivially possible anyway, and it would be unfortunate to force authors to use script to do them when sandboxed rather than allowing them to use the declarative features.

These flags must not be set unless the conditions listed above define them as being set.

These flags only take effect when the nested browsing context of the iframe is navigated. Removing them, or removing the entire sandbox attribute, has no effect on an already-loaded page.

In this example, some completely-unknown, potentially hostile, user-provided HTML content is embedded in a page. Because it is sandboxed, it is treated by the user agent as being from a unique origin, despite the content being served from the same site. Thus it is affected by all the normal cross-site restrictions. In addition, the embedded page has scripting disabled, plugins disabled, forms disabled, and it cannot navigate any frames or windows other than itself (or any frames or windows it itself embeds).

<p>We're not scared of you! Here is your content, unedited:</p>
<iframe sandbox src="getusercontent.cgi?id=12193"></iframe>

Note that cookies are still sent to the server in the getusercontent.cgi request, though they are not visible in the document.cookie IDL attribute.

It is important that the server serve the user-provided HTML using the text/html-sandboxed MIME type so that if the attacker convinces the user to visit that page directly, the page doesn't run in the context of the site's origin, which would make the user vulnerable to any attack found in the page.

In this example, a gadget from another site is embedded. The gadget has scripting and forms enabled, and the origin sandbox restrictions are lifted, allowing the gadget to communicate with its originating server. The sandbox is still useful, however, as it disables plugins and popups, thus reducing the risk of the user being exposed to malware and other annoyances.

<iframe sandbox="allow-same-origin allow-forms allow-scripts"
        src="http://maps.example.com/embedded.html"></iframe>

Suppose a file A contained the following fragment:

<iframe sandbox="allow-same-origin allow-forms" src=B></iframe>

Suppose that file B contained an iframe also:

<iframe sandbox="allow-scripts" src=C></iframe>

Further, suppose that file C contained a link:

<a href=D>Link</a>

For this example, suppose all the files were served as text/html.

Page C in this scenario has all the sandboxing flags set. Scripts are disabled, because the iframe in A has scripts disabled, and this overrides the allow-scripts keyword set on the iframe in B. Forms are also disabled, because the inner iframe (in B) does not have the allow-forms keyword set.

Suppose now that a script in A removes all the sandbox attributes in A and B. This would change nothing immediately. If the user clicked the link in C, loading page D into the iframe in B, page D would now act as if the iframe in B had the allow-same-origin and allow-forms keywords set, because that was the state of the nested browsing context in the iframe in A when page B was loaded.

Generally speaking, dynamically removing or changing the sandbox attribute is ill-advised, because it can make it quite hard to reason about what will be allowed and what will not.

Potentially hostile files can be served from the same server as the file containing the iframe element by labeling them as text/html-sandboxed instead of text/html. This ensures that scripts in the files are unable to attack the site (as if they were actually served from another server), even if the user is tricked into visiting those pages directly, without the protection of the sandbox attribute.

If the allow-scripts keyword is set along with allow-same-origin keyword, and the file is from the same origin as the iframe's Document, then a script in the "sandboxed" iframe could just reach out, remove the sandbox attribute, and then reload itself, effectively breaking out of the sandbox altogether.

The seamless attribute is a boolean attribute. When specified, it indicates that the iframe element's browsing context is to be rendered in a manner that makes it appear to be part of the containing document (seamlessly included in the parent document). Specifically, when the attribute is set on an iframe element whose owner Document's browsing context did not have the sandboxed seamless iframes flag set when that Document was created, and while either the browsing context's active document has the same origin as the iframe element's document, or the browsing context's active document's address has the same origin as the iframe element's document, or the browsing context's active document is an iframe srcdoc document, the following requirements apply:

The user agent must set the seamless browsing context flag to true for that browsing context. This will cause links to open in the parent browsing context unless an explicit self-navigation override is used (target="_self").
In a CSS-supporting user agent: the user agent must add all the style sheets that apply to the iframe element to the cascade of the active document of the iframe element's nested browsing context, at the appropriate cascade levels, before any style sheets specified by the document itself.
In a CSS-supporting user agent: the user agent must, for the purpose of CSS property inheritance only, treat the root element of the active document of the iframe element's nested browsing context as being a child of the iframe element. (Thus inherited properties on the root element of the document in the iframe will inherit the computed values of those properties on the iframe element instead of taking their initial values.)
In visual media, in a CSS-supporting user agent: the user agent should set the intrinsic width of the iframe to the width that the element would have if it was a non-replaced block-level element with 'width: auto'.
In visual media, in a CSS-supporting user agent: the user agent should set the intrinsic height of the iframe to the height of the bounding box around the content rendered in the iframe at its current width (as given in the previous bullet point), as it would be if the scrolling position was such that the top of the viewport for the content rendered in the iframe was aligned with the origin of that content's canvas.
In visual media, in a CSS-supporting user agent: the user agent must force the height of the initial containing block of the active document of the nested browsing context of the iframe to zero.

This is intended to get around the otherwise circular dependency of percentage dimensions that depend on the height of the containing block, thus affecting the height of the document's bounding box, thus affecting the height of the viewport, thus affecting the size of the initial containing block.
In speech media, the user agent should render the nested browsing context without announcing that it is a separate document.
User agents should, in general, act as if the active document of the iframe's nested browsing context was part of the document that the iframe is in, if any.

For example if the user agent supports listing all the links in a document, links in "seamlessly" nested documents would be included in that list without being significantly distinguished from links in the document itself.

If the attribute is not specified, or if the origin conditions listed above are not met, then the user agent should render the nested browsing context in a manner that is clearly distinguishable as a separate browsing context, and the seamless browsing context flag must be set to false for that browsing context.

It is important that user agents recheck the above conditions whenever the active document of the nested browsing context of the iframe changes, such that the seamless browsing context flag gets unset if the nested browsing context is navigated to another origin.

The attribute can be set or removed dynamically, with the rendering updating in tandem.

In this example, the site's navigation is embedded using a client-side include using an iframe. Any links in the iframe will, in new user agents, be automatically opened in the iframe's parent browsing context; for legacy user agents, the site could also include a base element with a target attribute with the value _parent. Similarly, in new user agents the styles of the parent page will be automatically applied to the contents of the frame, but to support legacy user agents authors might wish to include the styles explicitly.

<nav><iframe seamless src="nav.include.html"></iframe></nav>

The iframe element supports dimension attributes for cases where the embedded content has specific dimensions (e.g. ad units have well-defined dimensions).

An iframe element never has fallback content, as it will always create a nested browsing context, regardless of whether the specified initial contents are successfully used.

Descendants of iframe elements represent nothing. (In legacy user agents that do not support iframe elements, the contents would be parsed as markup that could act as fallback content.)

When used in HTML documents, the allowed content model of iframe elements is text, except that invoking the HTML fragment parsing algorithm with the iframe element as the context element and the text contents as the input must result in a list of nodes that are all phrasing content, with no parse errors having occurred, with no script elements being anywhere in the list or as descendants of elements in the list, and with all the elements in the list (including their descendants) being themselves conforming.

The iframe element must be empty in XML documents.

The HTML parser treats markup inside iframe elements as text.

The IDL attributes src, srcdoc, name, sandbox, and seamless must reflect the respective content attributes of the same name.

The contentDocument IDL attribute must return the Document object of the active document of the iframe element's nested browsing context.

The contentWindow IDL attribute must return the WindowProxy object of the iframe element's nested browsing context.

Here is an example of a page using an iframe to include advertising from an advertising broker:

<iframe src="http://ads.example.com/?customerid=923513721&amp;format=banner"
        width="468" height="60"></iframe>

4.8.3 The `embed` element

Categories

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

Empty.

Content attributes:

src

type

width

height

Any other attribute that has no namespace (see prose).

DOM interface:

interface HTMLEmbedElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute DOMString width;
           attribute DOMString height;
};

Depending on the type of content instantiated by the embed element, the node may also support other interfaces.

The embed element represents an integration point for an external (typically non-HTML) application or interactive content.

The src attribute gives the address of the resource being embedded. The attribute, if present, must contain a valid non-empty URL potentially surrounded by spaces.

The type attribute, if present, gives the MIME type by which the plugin to instantiate is selected. The value must be a valid MIME type. If both the type attribute and the src attribute are present, then the type attribute must specify the same type as the explicit Content-Type metadata of the resource given by the src attribute.

When the element is created with neither a src attribute nor a type attribute, and when attributes are removed such that neither attribute is present on the element anymore, and when the element has a media element ancestor, and when the element has an ancestor object element that is not showing its fallback content, any plugins instantiated for the element must be removed, and the embed element represents nothing.

If either:

the sandboxed plugins browsing context flag was set on the browsing context for which the embed element's Document is the active document when that Document was created, or
the embed element's Document was parsed from a resource whose sniffed type as determined during navigation is text/html-sandboxed

...then the user agent must render the embed element in a manner that conveys that the plugin was disabled. The user agent may offer the user the option to override the sandbox and instantiate the plugin anyway; if the user invokes such an option, the user agent must act as if the conditions above did not apply for the purposes of this element.

Plugins are disabled in sandboxed browsing contexts because they might not honor the restrictions imposed by the sandbox (e.g. they might allow scripting even when scripting in the sandbox is disabled). User agents should convey the danger of overriding the sandbox to the user if an option to do so is provided.

An embed element is said to be potentially active when the following conditions are all met simultaneously:

The element is in a Document.
The element's Document is fully active.
The element has either a src attribute set or a type attribute set (or both).
The element's src attribute is either absent or its value is the empty string.
The element is not in a Document whose browsing context had the sandboxed plugins browsing context flag set when the Document was created (unless this has been overridden as described above).
The element's Document was not parsed from a resource whose sniffed type as determined during navigation is text/html-sandboxed (unless this has been overridden as described above).
The element is not a descendant of a media element.
The element is not a descendant of an object element that is not showing its fallback content.

Whenever an embed element that was not potentially active becomes potentially active, and whenever a potentially active embed element's src attribute is set, changed, or removed, and whenever a potentially active embed element's type attribute is set, changed, or removed, the appropriate set of steps from the following is then applied:

If the element has a src attribute set

The user agent must resolve the value of the element's src attribute, relative to the element. If that is successful, the user agent should fetch the resulting absolute URL, from the element's browsing context scope origin if it has one. The task that is queued by the networking task source once the resource has been fetched must find and instantiate an appropriate plugin based on the content's type, and hand that plugin the content of the resource, replacing any previously instantiated plugin for the element.

Fetching the resource must delay the load event of the element's document.

If the element has no src attribute set

The user agent should find and instantiate an appropriate plugin based on the value of the type attribute.

Whenever an embed element that was potentially active stops being potentially active, any plugin that had been instantiated for that element must be unloaded.

The embed element is unaffected by the CSS 'display' property. The selected plugin is instantiated even if the element is hidden with a 'display:none' CSS style.

The type of the content being embedded is defined as follows:

If the element has a type attribute, and that attribute's value is a type that a plugin supports, then the value of the type attribute is the content's type.
Otherwise, if the <path> component of the URL of the specified resource (after any redirects) matches a pattern that a plugin supports, then the content's type is the type that that plugin can handle.

For example, a plugin might say that it can handle resources with <path> components that end with the four character string ".swf".
Otherwise, if the specified resource has explicit Content-Type metadata, then that is the content's type.
Otherwise, the content has no type and there can be no appropriate plugin for it.

The embed element has no fallback content. If the user agent can't find a suitable plugin, then the user agent must use a default plugin. (This default could be as simple as saying "Unsupported Format".)

Whether the resource is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the resource's type and when handing the resource to the plugin.

This allows servers to return data for plugins even with error responses (e.g. HTTP 500 Internal Server Error codes can still contain plugin data).

Any namespace-less attribute other than name, align, hspace, and vspace may be specified on the embed element, so long as its name is XML-compatible and contains no characters in the range U+0041 to U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z). These attributes are then passed as parameters to the plugin.

All attributes in HTML documents get lowercased automatically, so the restriction on uppercase letters doesn't affect such documents.

The four exceptions are to exclude legacy attributes that have side-effects beyond just sending parameters to the plugin.

The user agent should pass the names and values of all the attributes of the embed element that have no namespace to the plugin used, when it is instantiated.

If the plugin instantiated for the embed element supports a scriptable interface, the HTMLEmbedElement object representing the element should expose that interface while the element is instantiated.

The embed element supports dimension attributes.

The IDL attributes src and type each must reflect the respective content attributes of the same name.

Here's a way to embed a resource that requires a proprietary plug-in, like Flash:

<embed src="catgame.swf">

If the user does not have the plug-in (for example if the plug-in vendor doesn't support the user's platform), then the user will be unable to use the resource.

To pass the plugin a parameter "quality" with the value "high", an attribute can be specified:

<embed src="catgame.swf" quality="high">

This would be equivalent to the following, when using an object element instead:

<object data="catgame.swf">
 <param name="quality" value="high">
</object>

4.8.4 The `object` element

Categories

If the element has a usemap attribute: Interactive content.

Listed, submittable, form-associated element.

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

Zero or more param elements, then, transparent.

Content attributes:

data

type

name

usemap

form

width

height

DOM interface:

interface HTMLObjectElement : HTMLElement {
           attribute DOMString data;
           attribute DOMString type;
           attribute DOMString name;
           attribute DOMString useMap;
  readonly attribute HTMLFormElement form;
           attribute DOMString width;
           attribute DOMString height;
  readonly attribute Document contentDocument;
  readonly attribute WindowProxy contentWindow;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);
};

Depending on the type of content instantiated by the object element, the node also supports other interfaces.

The object element can represent an external resource, which, depending on the type of the resource, will either be treated as an image, as a nested browsing context, or as an external resource to be processed by a plugin.

The data attribute, if present, specifies the address of the resource. If present, the attribute must be a valid non-empty URL potentially surrounded by spaces.

The type attribute, if present, specifies the type of the resource. If present, the attribute must be a valid MIME type.

At least one of either the data attribute or the type attribute must be present.

The name attribute, if present, must be a valid browsing context name. The given value is used to name the nested browsing context, if applicable.

When the element is created, when it is popped off the stack of open elements of an HTML parser or XML parser, and subsequently whenever the element is inserted into a document or removed from a document; and whenever the element's Document changes whether it is fully active; and whenever an ancestor object element changes to or from showing its fallback content; and whenever the element's classid attribute is set, changed, or removed; and, when its classid attribute is not present, whenever its data attribute is set, changed, or removed; and, when neither its classid attribute nor its data attribute are present, whenever its type attribute is set, changed, or removed: the user agent must queue a task to run the following steps to (re)determine what the object element represents. The task source for this task is the DOM manipulation task source.

If the user has indicated a preference that this object element's fallback content be shown instead of the element's usual behavior, then jump to the last step in the overall set of steps (fallback).

For example, a user could ask for the element's fallback content to be shown because that content uses a format that the user finds more accessible.
If the element has an ancestor media element, or has an ancestor object element that is not showing its fallback content, or if the element is not in a Document with a browsing context, or if the element's Document is not fully active, or if the element is still in the stack of open elements of an HTML parser or XML parser, then jump to the last step in the overall set of steps (fallback).
If the classid attribute is present, and has a value that isn't the empty string, then: if the user agent can find a plugin suitable according to the value of the classid attribute, and plugins aren't being sandboxed, then that plugin should be used, and the value of the data attribute, if any, should be passed to the plugin. If no suitable plugin can be found, or if the plugin reports an error, jump to the last step in the overall set of steps (fallback).
If the data attribute is present and its value is not the empty string, then:
1. If the type attribute is present and its value is not a type that the user agent supports, and is not a type that the user agent can find a plugin for, then the user agent may jump to the last step in the overall set of steps (fallback) without fetching the content to examine its real type.
2. Resolve the URL specified by the data attribute, relative to the element.
3. If that failed, fire a simple event named error at the element, then jump to the last step in the overall set of steps (fallback).
4. Fetch the resulting absolute URL, from the element's browsing context scope origin if it has one.
  
  Fetching the resource must delay the load event of the element's document until the task that is queued by the networking task source once the resource has been fetched (defined next) has been run.
  
  For the purposes of the application cache networking model, this fetch operation is not for a child browsing context (though it might end up being used for one after all, as defined below).
5. If the resource is not yet available (e.g. because the resource was not available in the cache, so that loading the resource required making a request over the network), then jump to the last step in the overall set of steps (fallback). The task that is queued by the networking task source once the resource is available must restart this algorithm from this step. Resources can load incrementally; user agents may opt to consider a resource "available" whenever enough data has been obtained to begin processing the resource.
6. If the load failed (e.g. there was an HTTP 404 error, there was a DNS error), fire a simple event named error at the element, then jump to the last step in the overall set of steps (fallback).
7. Determine the resource type, as follows:
  1. Let the resource type be unknown.
  2. If the user agent is configured to strictly obey Content-Type headers for this resource, and the resource has associated Content-Type metadata, then let the resource type be the type specified in the resource's Content-Type metadata, and jump to the step below labeled handler.
  3. If there is a type attribute present on the object element, and that attribute's value is not a type that the user agent supports, but it is a type that a plugin supports, then let the resource type be the type specified in that type attribute, and jump to the step below labeled handler.
  4. Run the approprate set of steps from the following list:
    The resource has associated Content-Type metadata
    Let binary be false.
    
    If the type specified in the resource's Content-Type metadata is "text/plain", and the result of applying the rules for distinguishing if a resource is text or binary to the resource is that the resource is not text/plain, then set binary to true.
    
    If the type specified in the resource's Content-Type metadata is "application/octet-stream", then set binary to true.
    
    If binary is false, then let the resource type be the type specified in the resource's Content-Type metadata, and jump to the step below labeled handler.
    
    If there is a type attribute present on the object element, and its value is not application/octet-stream, then run the following steps:
    
    If the attribute's value is a type that a plugin supports, or the attribute's value is a type that starts with "image/" that is not also an XML MIME type, then let the resource type be the type specified in that type attribute.
    
    Jump to the step below labeled handler.
    The resource does not have associated Content-Type metadata
    If there is a type attribute present on the object element, then let the tentative type be the type specified in that type attribute.
    
    Otherwise, let tentative type be the sniffed type of the resource.
    
    If tentative type is not application/octet-stream, then let resource type be tentative type and jump to the step below labeled handler.
  5. If the <path> component of the URL of the specified resource (after any redirects) matches a pattern that a plugin supports, then let resource type be the type that that plugin can handle.
    
    For example, a plugin might say that it can handle resources with <path> components that end with the four character string ".swf".
  It is possible for this step to finish with resource type still being unknown, or for one of the substeps above to jump straight to the next step. In both cases, the next step will trigger fallback.
8. Handler: Handle the content as given by the first of the following cases that matches:
  
  If the resource type is not a type that the user agent supports, but it is a type that a plugin supports
  
  If plugins are being sandboxed, jump to the last step in the overall set of steps (fallback).
  
  Otherwise, the user agent should use the plugin that supports resource type and pass the content of the resource to that plugin. If the plugin reports an error, then jump to the last step in the overall set of steps (fallback).
  
  If the resource type is an XML MIME type, or if the resource type does not start with "image/"
  
  The object element must be associated with a newly created nested browsing context, if it does not already have one.
  
  If the URL of the given resource is not about:blank, the element's nested browsing context must then be navigated to that resource, with replacement enabled, and with the object element's document's browsing context as the source browsing context. (The data attribute of the object element doesn't get updated if the browsing context gets further navigated to other locations.)
  
  If the URL of the given resource is about:blank, then, instead, the user agent must queue a task to fire a simple event named load at the object element.
  
  The object element represents the nested browsing context.
  
  If the name attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.
  
  In certain situations, e.g. if the resource was fetched from an application cache but it is an HTML file with a manifest attribute that points to a different application cache manifest, the navigation of the browsing context will be restarted so as to load the resource afresh from the network or a different application cache. Even if the resource is then found to have a different type, it is still used as part of a nested browsing context: only the navigate algorithm is restarted, not this object algorithm.
  
  If the resource type starts with "image/", and support for images has not been disabled
  
  Apply the image sniffing rules to determine the type of the image.
  
  The object element represents the specified image. The image is not a nested browsing context.
  
  If the image cannot be rendered, e.g. because it is malformed or in an unsupported format, jump to the last step in the overall set of steps (fallback).
  
  Otherwise
  
  The given resource type is not supported. Jump to the last step in the overall set of steps (fallback).
  
  If the previous step ended with the resource type being unknown, this is the case that is triggered.
9. The element's contents are not part of what the object element represents.
10. Once the resource is completely loaded, queue a task to fire a simple event named load at the element.
  
  The task source for this task is the DOM manipulation task source.
If the data attribute is absent but the type attribute is present, plugins aren't being sandboxed, and the user agent can find a plugin suitable according to the value of the type attribute, then that plugin should be used. If no suitable plugin can be found, or if the plugin reports an error, jump to the next step (fallback).
(Fallback.) The object element represents the element's children, ignoring any leading param element children. This is the element's fallback content. If the element has an instantiated plugin, then unload it.

When the algorithm above instantiates a plugin, the user agent should pass to the plugin used the names and values of all the attributes on the element, in the order they were added to the element, with the attributes added by the parser being ordered in source order, followed by a parameter named "PARAM" whose value is null, followed by all the names and values of parameters given by param elements that are children of the object element, in tree order. If the plugin supports a scriptable interface, the HTMLObjectElement object representing the element should expose that interface. The object element represents the plugin. The plugin is not a nested browsing context.

If either:

the sandboxed plugins browsing context flag was set on the object element's Document's browsing context when the Document was created, or
the object element's Document was parsed from a resource whose sniffed type as determined during navigation is text/html-sandboxed

...then the steps above must always act as if they had failed to find a plugin, even if one would otherwise have been used.

The above algorithm is independent of CSS properties (including 'display', 'overflow', and 'visibility'). For example, it runs even if the element is hidden with a 'display:none' CSS style, and does not run again if the element's visibility changes.

Due to the algorithm above, the contents of object elements act as fallback content, used only when referenced resources can't be shown (e.g. because it returned a 404 error). This allows multiple object elements to be nested inside each other, targeting multiple user agents with different capabilities, with the user agent picking the first one it supports.

Whenever the name attribute is set, if the object element has a nested browsing context, its name must be changed to the new value. If the attribute is removed, if the object element has a browsing context, the browsing context name must be set to the empty string.

The usemap attribute, if present while the object element represents an image, can indicate that the object has an associated image map. The attribute must be ignored if the object element doesn't represent an image.

The form attribute is used to explicitly associate the object element with its form owner.

Constraint validation: object elements are always barred from constraint validation.

The object element supports dimension attributes.

The IDL attributes data, type, name, and useMap each must reflect the respective content attributes of the same name.

The contentDocument IDL attribute must return the Document object of the active document of the object element's nested browsing context, if it has one; otherwise, it must return null.

The contentWindow IDL attribute must return the WindowProxy object of the object element's nested browsing context, if it has one; otherwise, it must return null.

In the following example, a Java applet is embedded in a page using the object element. (Generally speaking, it is better to avoid using applets like these and instead use native JavaScript and HTML to provide the functionality, since that way the application will work on all Web browsers without requiring a third-party plugin. Many devices, especially embedded devices, do not support third-party technologies like Java.)

<figure>
 <object type="application/x-java-applet">
  <param name="code" value="MyJavaClass">
  <p>You do not have Java available, or it is disabled.</p>
 </object>
 <figcaption>My Java Clock</figcaption>
</figure>

In this example, an HTML page is embedded in another using the object element.

<figure>
 <object data="clock.html"></object>
 <figcaption>My HTML Clock</figcaption>
</figure>

The following example shows how a plugin can be used in HTML (in this case the Flash plugin, to show a video file). Fallback is provided for users who do not have Flash enabled, in this case using the video element to show the video for those using user agents that support video, and finally providing a link to the video for those who have neither Flash nor a video-capable browser.

<p>Look at my video:
 <object type="application/x-shockwave-flash">
  <param name=movie value="http://video.example.com/library/watch.swf">
  <param name=allowfullscreen value=true>
  <param name=flashvars value="http://video.example.com/vids/315981">
  <video controls src="http://video.example.com/vids/315981">
   <a href="http://video.example.com/vids/315981">View video</a>.
  </video>
 </object>
</p>

4.8.5 The `param` element

Categories

None.

Contexts in which this element can be used:

As a child of an object element, before any flow content.

Content model:

Empty.

Content attributes:

name

value

DOM interface:

interface HTMLParamElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString value;
};

The param element defines parameters for plugins invoked by object elements. It does not represent anything on its own.

The name attribute gives the name of the parameter.

The value attribute gives the value of the parameter.

Both attributes must be present. They may have any value.

If both attributes are present, and if the parent element of the param is an object element, then the element defines a parameter with the given name/value pair.

If either the name or value of a parameter defined by a param element that is the child of an object element that represents an instantiated plugin changes, and if that plugin is communicating with the user agent using an API that features the ability to update the plugin when the name or value of a parameter so changes, then the user agent must appropriately exercise that ability to notify the plugin of the change.

The IDL attributes name and value must both reflect the respective content attributes of the same name.

The following example shows how the param element can be used to pass a parameter to a plugin, in this case the O3D plugin.

<!DOCTYPE HTML>
<html lang="en">
  <head>
   <title>O3D Utah Teapot</title>
  </head>
  <body>
   <p>
    <object type="application/vnd.o3d.auto">
     <param name="o3d_features" value="FloatingPointTextures">
     <img src="o3d-teapot.png"
          title="3D Utah Teapot illustration rendered using O3D."
          alt="When O3D renders the Utah Teapot, it appears as a squat
          teapot with a shiny metallic finish on which the
          surroundings are reflected, with a faint shadow caused by
          the lighting.">
     <p>To see the teapot actually rendered by O3D on your
     computer, please download and install the <a
     href="http://code.google.com/apis/o3d/docs/gettingstarted.html#install">O3D plugin</a>.</p>
    </object>
    <script src="o3d-teapot.js"></script>
   </p>
  </body>
</html>

4.8.6 The `video` element

Categories

If the element has a controls attribute: Interactive content.

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

If the element has a src attribute: zero or more track elements, then transparent, but with no media element descendants.

If the element does not have a src attribute: zero or more source elements, then zero or more track elements, then transparent, but with no media element descendants.

Content attributes:

src

poster

preload

autoplay

mediagroup

loop

muted

controls

width

height

DOM interface:

interface HTMLVideoElement : HTMLMediaElement {
           attribute unsigned long width;
           attribute unsigned long height;
  readonly attribute unsigned long videoWidth;
  readonly attribute unsigned long videoHeight;
           attribute DOMString poster;
};

A video element is used for playing videos or movies, and audio files with captions.

Content may be provided inside the video element. User agents should not show this content to the user; it is intended for older Web browsers which do not support video, so that legacy video plugins can be tried, or to show text to the users of these older browsers informing them of how to access the video contents.

In particular, this content is not intended to address accessibility concerns. To make video content accessible to the blind, deaf, and those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as caption or subtitle tracks, audio description tracks, or sign-language overlays) into their media streams.

The video element is a media element whose media data is ostensibly video data, possibly with associated audio data.

The src, preload, autoplay, mediagroup, loop, muted, and controls attributes are the attributes common to all media elements.

The poster attribute gives the address of an image file that the user agent can show while no video data is available. The attribute, if present, must contain a valid non-empty URL potentially surrounded by spaces.

If the specified resource is to be used, then, when the element is created or when the poster attribute is set, changed, or removed, the user agent must run the following steps to determine the element's poster frame:

If there is an existing instance of this algorithm running for this video element, abort that instance of this algorithm without changing the poster frame.
If the poster attribute's value is the empty string or if the attribute is absent, then there is no poster frame; abort these steps.
Resolve the poster attribute's value relative to the element. If this fails, then there is no poster frame; abort these steps.
Fetch the resulting absolute URL, from the element's Document's origin. This must delay the load event of the element's document.
If an image is thus obtained, the poster frame is that image. Otherwise, there is no poster frame.

The image given by the poster attribute, the poster frame, is intended to be a representative frame of the video (typically one of the first non-blank frames) that gives the user an idea of what the video is like.

When no video data is available (the element's readyState attribute is either HAVE_NOTHING, or HAVE_METADATA but no video data has yet been obtained at all, or the element's readyState attribute is any subsequent value but the media resource does not have a video channel), the video element represents either the poster frame, or nothing.

When a video element is paused and the current playback position is the first frame of video, the element represents either the frame of video corresponding to the current playback position or the poster frame, at the discretion of the user agent.

Notwithstanding the above, the poster frame should be preferred over nothing, but the poster frame should not be shown again after a frame of video has been shown.

When a video element is paused at any other position, and the media resource has a video channel, the element represents the frame of video corresponding to the current playback position, or, if that is not yet available (e.g. because the video is seeking or buffering), the last frame of the video to have been rendered.

When a video element whose media resource has a video channel is potentially playing, it represents the frame of video at the continuously increasing "current" position. When the current playback position changes such that the last frame rendered is no longer the frame corresponding to the current playback position in the video, the new frame must be rendered. Similarly, any audio associated with the media resource must, if played, be played synchronized with the current playback position, at the element's effective media volume.

When a video element whose media resource has a video channel is neither potentially playing nor paused (e.g. when seeking or stalled), the element represents the last frame of the video to have been rendered.

Which frame in a video stream corresponds to a particular playback position is defined by the video stream's format.

The video element also represents any text track cues whose text track cue active flag is set and whose text track is in the showing or showing by default modes.

In addition to the above, the user agent may provide messages to the user (such as "buffering", "no video loaded", "error", or more detailed information) by overlaying text or icons on the video or other areas of the element's playback area, or in another appropriate manner.

User agents that cannot render the video may instead make the element represent a link to an external video playback utility or to the video data itself.

video . videoWidth
video . videoHeight: These attributes return the intrinsic dimensions of the video, or zero if the dimensions are not known.

The intrinsic width and intrinsic height of the media resource are the dimensions of the resource in CSS pixels after taking into account the resource's dimensions, aspect ratio, clean aperture, resolution, and so forth, as defined for the format used by the resource. If an anamorphic format does not define how to apply the aspect ratio to the video data's dimensions to obtain the "correct" dimensions, then the user agent must apply the ratio by increasing one dimension and leaving the other unchanged.

The videoWidth IDL attribute must return the intrinsic width of the video in CSS pixels. The videoHeight IDL attribute must return the intrinsic height of the video in CSS pixels. If the element's readyState attribute is HAVE_NOTHING, then the attributes must return 0.

The video element supports dimension attributes.

In the absence of style rules to the contrary, video content should be rendered inside the element's playback area such that the video content is shown centered in the playback area at the largest possible size that fits completely within it, with the video content's aspect ratio being preserved. Thus, if the aspect ratio of the playback area does not match the aspect ratio of the video, the video will be shown letterboxed or pillarboxed. Areas of the element's playback area that do not contain the video represent nothing.

In user agents that implement CSS, the above requirement can be implemented by using the style rule suggested in the rendering section.

The intrinsic width of a video element's playback area is the intrinsic width of the video resource, if that is available; otherwise it is the intrinsic width of the poster frame, if that is available; otherwise it is 300 CSS pixels.

The intrinsic height of a video element's playback area is the intrinsic height of the video resource, if that is available; otherwise it is the intrinsic height of the poster frame, if that is available; otherwise it is 150 CSS pixels.

User agents should provide controls to enable or disable the display of closed captions, audio description tracks, and other additional data associated with the video stream, though such features should, again, not interfere with the page's normal rendering.

User agents may allow users to view the video content in manners more suitable to the user (e.g. full-screen or in an independent resizable window). As for the other user interface features, controls to enable this should not interfere with the page's normal rendering unless the user agent is exposing a user interface. In such an independent context, however, user agents may make full user interfaces visible, with, e.g., play, pause, seeking, and volume controls, even if the controls attribute is absent.

User agents may allow video playback to affect system features that could interfere with the user's experience; for example, user agents could disable screensavers while video playback is in progress.

The poster IDL attribute must reflect the poster content attribute.

This example shows how to detect when a video has failed to play correctly:

<script>
 function failed(e) {
   // video playback failed - show a message saying why
   switch (e.target.error.code) {
     case e.target.error.MEDIA_ERR_ABORTED:
       alert('You aborted the video playback.');
       break;
     case e.target.error.MEDIA_ERR_NETWORK:
       alert('A network error caused the video download to fail part-way.');
       break;
     case e.target.error.MEDIA_ERR_DECODE:
       alert('The video playback was aborted due to a corruption problem or because the video used features your browser did not support.');
       break;
     case e.target.error.MEDIA_ERR_SRC_NOT_SUPPORTED:
       alert('The video could not be loaded, either because the server or network failed or because the format is not supported.');
       break;
     default:
       alert('An unknown error occurred.');
       break;
   }
 }
</script>
<p><video src="tgif.vid" autoplay controls onerror="failed(event)"></video></p>
<p><a href="tgif.vid">Download the video file</a>.</p>

4.8.7 The `audio` element

Categories

If the element has a controls attribute: Interactive content.

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

If the element has a src attribute: zero or more track elements, then transparent, but with no media element descendants.

If the element does not have a src attribute: one or more source elements, then zero or more track elements, then transparent, but with no media element descendants.

Content attributes:

src

preload

autoplay

mediagroup

loop

muted

controls

DOM interface:

[NamedConstructor=Audio(),
 NamedConstructor=Audio(in DOMString src)]
interface HTMLAudioElement : HTMLMediaElement {};

An audio element represents a sound or audio stream.

Content may be provided inside the audio element. User agents should not show this content to the user; it is intended for older Web browsers which do not support audio, so that legacy audio plugins can be tried, or to show text to the users of these older browsers informing them of how to access the audio contents.

In particular, this content is not intended to address accessibility concerns. To make audio content accessible to the deaf or to those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as transcriptions) into their media streams.

The audio element is a media element whose media data is ostensibly audio data.

The src, preload, autoplay, mediagroup, loop, muted, and controls attributes are the attributes common to all media elements.

When an audio element is potentially playing, it must have its audio data played synchronized with the current playback position, at the element's effective media volume.

When an audio element is not potentially playing, audio must not play for the element.

audio = new Audio( [ url ] ): Returns a new audio element, with the src attribute set to the value passed in the argument, if applicable.

Two constructors are provided for creating HTMLAudioElement objects (in addition to the factory methods from DOM Core such as createElement()): Audio() and Audio(src). When invoked as constructors, these must return a new HTMLAudioElement object (a new audio element). The element must have its preload attribute set to the literal value "auto". If the src argument is present, the object created must have its src content attribute set to the provided value, and the user agent must invoke the object's resource selection algorithm before returning. The element's document must be the active document of the browsing context of the Window object on which the interface object of the invoked constructor is found.

4.8.8 The `source` element

Categories

None.

Contexts in which this element can be used:

As a child of a media element, before any flow content or track elements.

Content model:

Empty.

Content attributes:

src

type

media

DOM interface:

interface HTMLSourceElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute DOMString media;
};

The source element allows authors to specify multiple alternative media resources for media elements. It does not represent anything on its own.

The src attribute gives the address of the media resource. The value must be a valid non-empty URL potentially surrounded by spaces. This attribute must be present.

Dynamically modifying a source element and its attribute when the element is already inserted in a video or audio element will have no effect. To change what is playing, either just use the src attribute on the media element directly, or call the load() method on the media element after manipulating the source elements.

The type attribute gives the type of the media resource, to help the user agent determine if it can play this media resource before fetching it. If specified, its value must be a valid MIME type. The codecs parameter, which certain MIME types define, might be necessary to specify exactly how the resource is encoded. [RFC4281]

The following list shows some examples of how to use the codecs= MIME parameter in the type attribute.

H.264 Constrained baseline profile video (main and extended video compatible) level 3 and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="avc1.42E01E, mp4a.40.2"'>

H.264 Extended profile video (baseline-compatible) level 3 and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="avc1.58A01E, mp4a.40.2"'>

H.264 Main profile video level 3 and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="avc1.4D401E, mp4a.40.2"'>

H.264 'High' profile video (incompatible with main, baseline, or extended profiles) level 3 and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="avc1.64001E, mp4a.40.2"'>

MPEG-4 Visual Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="mp4v.20.8, mp4a.40.2"'>

MPEG-4 Advanced Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container

<source src='video.mp4' type='video/mp4; codecs="mp4v.20.240, mp4a.40.2"'>

MPEG-4 Visual Simple Profile Level 0 video and AMR audio in 3GPP container

<source src='video.3gp' type='video/3gpp; codecs="mp4v.20.8, samr"'>

Theora video and Vorbis audio in Ogg container

<source src='video.ogv' type='video/ogg; codecs="theora, vorbis"'>

Theora video and Speex audio in Ogg container

<source src='video.ogv' type='video/ogg; codecs="theora, speex"'>

Vorbis audio alone in Ogg container

<source src='audio.ogg' type='audio/ogg; codecs=vorbis'>

Speex audio alone in Ogg container

<source src='audio.spx' type='audio/ogg; codecs=speex'>

FLAC audio alone in Ogg container

<source src='audio.oga' type='audio/ogg; codecs=flac'>

Dirac video and Vorbis audio in Ogg container

<source src='video.ogv' type='video/ogg; codecs="dirac, vorbis"'>

The media attribute gives the intended media type of the media resource, to help the user agent determine if this media resource is useful to the user before fetching it. Its value must be a valid media query.

The default, if the media attribute is omitted, is "all", meaning that by default the media resource is suitable for all media.

If a source element is inserted as a child of a media element that has no src attribute and whose networkState has the value NETWORK_EMPTY, the user agent must invoke the media element's resource selection algorithm.

The IDL attributes src, type, and media must reflect the respective content attributes of the same name.

If the author isn't sure if the user agents will all be able to render the media resources provided, the author can listen to the error event on the last source element and trigger fallback behavior:

<script>
 function fallback(video) {
   // replace <video> with its contents
   while (video.hasChildNodes()) {
     if (video.firstChild instanceof HTMLSourceElement)
       video.removeChild(video.firstChild);
     else
       video.parentNode.insertBefore(video.firstChild, video);
   }
   video.parentNode.removeChild(video);
 }
</script>
<video controls autoplay>
 <source src='video.mp4' type='video/mp4; codecs="avc1.42E01E, mp4a.40.2"'>
 <source src='video.ogv' type='video/ogg; codecs="theora, vorbis"'
         onerror="fallback(parentNode)">
 ...
</video>

4.8.9 The `track` element

Categories

None.

Contexts in which this element can be used:

As a child of a media element, before any flow content.

Content model:

Empty.

Content attributes:

kind

src

srclang

label

default

DOM interface:

interface HTMLTrackElement : HTMLElement {
           attribute DOMString kind;
           attribute DOMString src;
           attribute DOMString srclang;
           attribute DOMString label;
           attribute boolean default;

  readonly attribute TextTrack track;
};

The track element allows authors to specify explicit external timed text tracks for media elements. It does not represent anything on its own.

The kind attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The keyword given in the first cell of each row maps to the state given in the second cell.

Keyword	State	Brief description
`subtitles`	Subtitles	Transcription or translation of the dialogue, suitable for when the sound is available but not understood (e.g. because the user does not understand the language of the media resource's soundtrack). Displayed over the video.
`captions`	Captions	Transcription or translation of the dialogue, sound effects, relevant musical cues, and other relevant audio information, suitable for when the soundtrack is unavailable (e.g. because it is muted or because the user is deaf). Displayed over the video; labeled as appropriate for the hard-of-hearing.
`descriptions`	Descriptions	Textual descriptions of the video component of the media resource, intended for audio synthesis when the visual component is unavailable (e.g. because the user is interacting with the application without a screen while driving, or because the user is blind). Synthesized as separate audio track.
`chapters`	Chapters	Chapter titles, intended to be used for navigating the media resource. Displayed as an interactive list in the user agent's interface.
`metadata`	Metadata	Tracks intended for use from script. Not displayed by the user agent.

The attribute may be omitted. The missing value default is the subtitles state.

The src attribute gives the address of the text track data. The value must be a valid non-empty URL potentially surrounded by spaces. This attribute must be present.

If the element has a src attribute whose value is not the empty string and whose value, when the attribute was set, could be successfully resolved relative to the element, then the element's track URL is the resulting absolute URL. Otherwise, the element's track URL is the empty string.

The srclang attribute gives the language of the text track data. The value must be a valid BCP 47 language tag. This attribute must be present if the element's kind attribute is in the subtitles state. [BCP47]

If the element has a srclang attribute whose value is not the empty string, then the element's track language is the value of the attribute. Otherwise, the element has no track language.

The label attribute gives a user-readable title for the track. This title is used by user agents when listing subtitle, caption, and audio description tracks in their user interface.

The value of the label attribute, if the attribute is present, must not be the empty string. Furthermore, there must not be two track element children of the same media element whose kind attributes are in the same state, whose srclang attributes are both missing or have values that represent the same language, and whose label attributes are again both missing or both have the same value.

If the element has a label attribute whose value is not the empty string, then the element's track label is the value of the attribute. Otherwise, the element's track label is a user-agent defined string (e.g. the string "untitled" in the user's locale, or a value automatically generated from the other attributes).

The default attribute, if specified, indicates that the track is to be enabled if the user's preferences do not indicate that another track would be more appropriate. There must not be more than one track element with the same parent node with the default attribute specified.

track . track: Returns the TextTrack object corresponding to the text track of the track element.

The track IDL attribute must, on getting, return the track element's text track's corresponding TextTrack object.

The src, srclang, label, and default IDL attributes must reflect the respective content attributes of the same name. The kind IDL attribute must reflect the content attribute of the same name, limited to only known values.

This video has subtitles in several languages:

<video src="brave.webm">
 <track kind=subtitles src=brave.en.vtt srclang=en label="English">
 <track kind=captions src=brave.en.vtt srclang=en label="English for the Hard of Hearing">
 <track kind=subtitles src=brave.fr.vtt srclang=fr label="Français">
 <track kind=subtitles src=brave.de.vtt srclang=de label="Deutsch">
</video>

4.8.10 Media elements

Media elements (audio and video, in this specification) implement the following interface:

interface HTMLMediaElement : HTMLElement {

  // error state
  readonly attribute MediaError error;

  // network state
           attribute DOMString src;
  readonly attribute DOMString currentSrc;
  const unsigned short NETWORK_EMPTY = 0;
  const unsigned short NETWORK_IDLE = 1;
  const unsigned short NETWORK_LOADING = 2;
  const unsigned short NETWORK_NO_SOURCE = 3;
  readonly attribute unsigned short networkState;
           attribute DOMString preload;
  readonly attribute TimeRanges buffered;
  void load();
  DOMString canPlayType(in DOMString type);

  // ready state
  const unsigned short HAVE_NOTHING = 0;
  const unsigned short HAVE_METADATA = 1;
  const unsigned short HAVE_CURRENT_DATA = 2;
  const unsigned short HAVE_FUTURE_DATA = 3;
  const unsigned short HAVE_ENOUGH_DATA = 4;
  readonly attribute unsigned short readyState;
  readonly attribute boolean seeking;

  // playback state
           attribute double currentTime;
  readonly attribute double initialTime;
  readonly attribute double duration;
  readonly attribute Date startOffsetTime;
  readonly attribute boolean paused;
           attribute double defaultPlaybackRate;
           attribute double playbackRate;
  readonly attribute TimeRanges played;
  readonly attribute TimeRanges seekable;
  readonly attribute boolean ended;
           attribute boolean autoplay;
           attribute boolean loop;
  void play();
  void pause();

  // media controller
           attribute DOMString mediaGroup;
           attribute MediaController controller;

  // controls
           attribute boolean controls;
           attribute double volume;
           attribute boolean muted;
           attribute boolean defaultMuted;

  // tracks
  readonly attribute MultipleTrackList audioTracks;
  readonly attribute ExclusiveTrackList videoTracks;
  readonly attribute TextTrack[] textTracks;
  MutableTextTrack addTextTrack(in DOMString kind, in optional DOMString label, in optional DOMString language);
};

The media element attributes, src, preload, autoplay, mediagroup, loop, muted, and controls, apply to all media elements. They are defined in this section.

Media elements are used to present audio data, or video and audio data, to the user. This is referred to as media data in this section, since this section applies equally to media elements for audio or for video. The term media resource is used to refer to the complete set of media data, e.g. the complete video file, or complete audio file.

A media resource can have multiple audio and video tracks. For the purposes of a media element, the video data of the media resource is only that of the currently selected track (if any) given by the element's videoTracks attribute, and the audio data of the media resource is the result of mixing all the currently enabled tracks (if any) given by the element's audioTracks attribute.

Both audio and video elements can be used for both audio and video. The main difference between the two is simply that the audio element has no playback area for visual content (such as video or captions), whereas the video element does.

Except where otherwise specified, the task source for all the tasks queued in this section and its subsections is the media element event task source.

4.8.10.1 Error codes

media . error

Returns a MediaError object representing the current error state of the element.

Returns null if there is no error.

All media elements have an associated error status, which records the last error the element encountered since its resource selection algorithm was last invoked. The error attribute, on getting, must return the MediaError object created for this last error, or null if there has not been an error.

interface MediaError {
  const unsigned short MEDIA_ERR_ABORTED = 1;
  const unsigned short MEDIA_ERR_NETWORK = 2;
  const unsigned short MEDIA_ERR_DECODE = 3;
  const unsigned short MEDIA_ERR_SRC_NOT_SUPPORTED = 4;
  readonly attribute unsigned short code;
};

media . error . code: Returns the current error's error code, from the list below.

The code attribute of a MediaError object must return the code for the error, which must be one of the following:

MEDIA_ERR_ABORTED (numeric value 1): The fetching process for the media resource was aborted by the user agent at the user's request.
MEDIA_ERR_NETWORK (numeric value 2): A network error of some description caused the user agent to stop fetching the media resource, after the resource was established to be usable.
MEDIA_ERR_DECODE (numeric value 3): An error of some description occurred while decoding the media resource, after the resource was established to be usable.
MEDIA_ERR_SRC_NOT_SUPPORTED (numeric value 4): The media resource indicated by the src attribute was not suitable.

4.8.10.2 Location of the media resource

The src content attribute on media elements gives the address of the media resource (video, audio) to show. The attribute, if present, must contain a valid non-empty URL potentially surrounded by spaces.

If a src attribute of a media element is set or changed, the user agent must invoke the media element's media element load algorithm. (Removing the src attribute does not do this, even if there are source elements present.)

The src IDL attribute on media elements must reflect the content attribute of the same name.

media . currentSrc

Returns the address of the current media resource.

Returns the empty string when there is no media resource.

The currentSrc IDL attribute is initially the empty string. Its value is changed by the resource selection algorithm defined below.

There are two ways to specify a media resource, the src attribute, or source elements. The attribute overrides the elements.

4.8.10.3 MIME types

A media resource can be described in terms of its type, specifically a MIME type, in some cases with a codecs parameter. (Whether the codecs parameter is allowed or not depends on the MIME type.) [RFC4281]

Types are usually somewhat incomplete descriptions; for example "video/mpeg" doesn't say anything except what the container type is, and even a type like "video/mp4; codecs="avc1.42E01E, mp4a.40.2"" doesn't include information like the actual bitrate (only the maximum bitrate). Thus, given a type, a user agent can often only know whether it might be able to play media of that type (with varying levels of confidence), or whether it definitely cannot play media of that type.

A type that the user agent knows it cannot render is one that describes a resource that the user agent definitely does not support, for example because it doesn't recognize the container type, or it doesn't support the listed codecs.

The MIME type "application/octet-stream" with no parameters is never a type that the user agent knows it cannot render. User agents must treat that type as equivalent to the lack of any explicit Content-Type metadata when it is used to label a potential media resource.

"application/octet-stream" is special-cased here; if any parameter appears with it, it should be treated just like any other MIME type. This is a deviation from the rule that unknown MIME type parameters should be ignored.

media . canPlayType(type): Returns the empty string (a negative response), "maybe", or "probably" based on how confident the user agent is that it can play media resources of the given type.

The canPlayType(type) method must return the empty string if type is a type that the user agent knows it cannot render or is the type "application/octet-stream"; it must return "probably" if the user agent is confident that the type represents a media resource that it can render if used in with this audio or video element; and it must return "maybe" otherwise. Implementors are encouraged to return "maybe" unless the type can be confidently established as being supported or not. Generally, a user agent should never return "probably" for a type that allows the codecs parameter if that parameter is not present.

This script tests to see if the user agent supports a (fictional) new format to dynamically decide whether to use a video element or a plugin:

<section id="video">
 <p><a href="playing-cats.nfv">Download video</a></p>
</section>
<script>
 var videoSection = document.getElementById('video');
 var videoElement = document.createElement('video');
 var support = videoElement.canPlayType('video/x-new-fictional-format;codecs="kittens,bunnies"');
 if (support != "probably" && "New Fictional Video Plug-in" in navigator.plugins) {
   // not confident of browser support
   // but we have a plugin
   // so use plugin instead
   videoElement = document.createElement("embed");
 } else if (support == "") {
   // no support from browser and no plugin
   // do nothing
   videoElement = null;
 }
 if (videoElement) {
   while (videoSection.hasChildNodes())
     videoSection.removeChild(videoSection.firstChild);
   videoElement.setAttribute("src", "playing-cats.nfv");
   videoSection.appendChild(videoElement);
 }
</script>

The type attribute of the source element allows the user agent to avoid downloading resources that use formats it cannot render.

4.8.10.4 Network states

media . networkState: Returns the current state of network activity for the element, from the codes in the list below.

As media elements interact with the network, their current network activity is represented by the networkState attribute. On getting, it must return the current network state of the element, which must be one of the following values:

NETWORK_EMPTY (numeric value 0): The element has not yet been initialized. All attributes are in their initial states.
NETWORK_IDLE (numeric value 1): The element's resource selection algorithm is active and has selected a resource, but it is not actually using the network at this time.
NETWORK_LOADING (numeric value 2): The user agent is actively trying to download data.
NETWORK_NO_SOURCE (numeric value 3): The element's resource selection algorithm is active, but it has not yet found a resource to use.

The resource selection algorithm defined below describes exactly when the networkState attribute changes value and what events fire to indicate changes in this state.

4.8.10.5 Loading the media resource

media . load(): Causes the element to reset and start selecting and loading a new media resource from scratch.

All media elements have an autoplaying flag, which must begin in the true state, and a delaying-the-load-event flag, which must begin in the false state. While the delaying-the-load-event flag is true, the element must delay the load event of its document.

When the load() method on a media element is invoked, the user agent must run the media element load algorithm.

The media element load algorithm consists of the following steps.

Abort any already-running instance of the resource selection algorithm for this element.
If there are any tasks from the media element's media element event task source in one of the task queues, then remove those tasks.

Basically, pending events and callbacks for the media element are discarded when the media element starts loading a new resource.
If the media element's networkState is set to NETWORK_LOADING or NETWORK_IDLE, queue a task to fire a simple event named abort at the media element.
If the media element's networkState is not set to NETWORK_EMPTY, then run these substeps:
1. Queue a task to fire a simple event named emptied at the media element.
2. If a fetching process is in progress for the media element, the user agent should stop it.
3. Set the networkState attribute to NETWORK_EMPTY.
4. Forget the media element's media-resource-specific text tracks.
5. If readyState is not set to HAVE_NOTHING, then set it to that state.
6. If the paused attribute is false, then set it to true.
7. If seeking is true, set it to false.
8. Set the current playback position to 0.
  
  If this changed the current playback position, then queue a task to fire a simple event named timeupdate at the media element.
9. Set the initial playback position to 0.
10. Set the timeline offset to Not-a-Number (NaN).
11. Update the duration attribute to Not-a-Number (NaN).
  
  The user agent will not fire a durationchange event for this particular change of the duration.
Set the playbackRate attribute to the value of the defaultPlaybackRate attribute.
Set the error attribute to null and the autoplaying flag to true.
Invoke the media element's resource selection algorithm.
Playback of any previously playing media resource for this element stops.

The resource selection algorithm for a media element is as follows. This algorithm is always invoked synchronously, but one of the first steps in the algorithm is to return and continue running the remaining steps asynchronously, meaning that it runs in the background with scripts and other tasks running in parallel. In addition, this algorithm interacts closely with the event loop mechanism; in particular, it has synchronous sections (which are triggered as part of the event loop algorithm). Steps in such sections are marked with ⌛.

Set the networkState to NETWORK_NO_SOURCE.
Asynchronously await a stable state, allowing the task that invoked this algorithm to continue. The synchronous section consists of all the remaining steps of this algorithm until the algorithm says the synchronous section has ended. (Steps in synchronous sections are marked with ⌛.)
⌛ If the media element has a src attribute, then let mode be attribute.

⌛ Otherwise, if the media element does not have a src attribute but has a source element child, then let mode be children and let candidate be the first such source element child in tree order.

⌛ Otherwise the media element has neither a src attribute nor a source element child: set the networkState to NETWORK_EMPTY, and abort these steps; the synchronous section ends.
⌛ Set the media element's delaying-the-load-event flag to true (this delays the load event), and set its networkState to NETWORK_LOADING.
⌛ Queue a task to fire a simple event named loadstart at the media element.
If mode is attribute, then run these substeps:
1. ⌛ Process candidate: If the src attribute's value is the empty string, then end the synchronous section, and jump down to the failed step below.
2. ⌛ Let absolute URL be the absolute URL that would have resulted from resolving the URL specified by the src attribute's value relative to the media element when the src attribute was last changed.
3. ⌛ If absolute URL was obtained successfully, set the currentSrc attribute to absolute URL.
4. End the synchronous section, continuing the remaining steps asynchronously.
5. If absolute URL was obtained successfully, run the resource fetch algorithm with absolute URL. If that algorithm returns without aborting this one, then the load failed.
6. Failed: Reaching this step indicates that the media resource failed to load or that the given URL could not be resolved. In one atomic operation, run the following steps:
  1. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_SRC_NOT_SUPPORTED.
  2. Forget the media element's media-resource-specific text tracks.
  3. Set the element's networkState attribute to the NETWORK_NO_SOURCE value.
7. Queue a task to fire a simple event named error at the media element.
8. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
9. Abort these steps. Until the load() method is invoked or the src attribute is changed, the element won't attempt to load another resource.
Otherwise, the source elements will be used; run these substeps:
1. ⌛ Let pointer be a position defined by two adjacent nodes in the media element's child list, treating the start of the list (before the first child in the list, if any) and end of the list (after the last child in the list, if any) as nodes in their own right. One node is the node before pointer, and the other node is the node after pointer. Initially, let pointer be the position between the candidate node and the next node, if there are any, or the end of the list, if it is the last node.
  
  As nodes are inserted and removed into the media element, pointer must be updated as follows:
  
  If a new node is inserted between the two nodes that define pointer
  
  Let pointer be the point between the node before pointer and the new node. In other words, insertions at pointer go after pointer.
  
  If the node before pointer is removed
  
  Let pointer be the point between the node after pointer and the node before the node after pointer. In other words, pointer doesn't move relative to the remaining nodes.
  
  If the node after pointer is removed
  
  Let pointer be the point between the node before pointer and the node after the node before pointer. Just as with the previous case, pointer doesn't move relative to the remaining nodes.
  
  Other changes don't affect pointer.
2. ⌛ Process candidate: If candidate does not have a src attribute, or if its src attribute's value is the empty string, then end the synchronous section, and jump down to the failed step below.
3. ⌛ Let absolute URL be the absolute URL that would have resulted from resolving the URL specified by candidate's src attribute's value relative to the candidate when the src attribute was last changed.
4. ⌛ If absolute URL was not obtained successfully, then end the synchronous section, and jump down to the failed step below.
5. ⌛ If candidate has a type attribute whose value, when parsed as a MIME type (including any codecs described by the codecs parameter, for types that define that parameter), represents a type that the user agent knows it cannot render, then end the synchronous section, and jump down to the failed step below.
6. ⌛ If candidate has a media attribute whose value does not match the environment, then end the synchronous section, and jump down to the failed step below.
7. ⌛ Set the currentSrc attribute to absolute URL.
8. End the synchronous section, continuing the remaining steps asynchronously.
9. Run the resource fetch algorithm with absolute URL. If that algorithm returns without aborting this one, then the load failed.
10. Failed: Queue a task to fire a simple event named error at the candidate element, in the context of the fetching process that was used to try to obtain candidate's corresponding media resource in the resource fetch algorithm.
11. Asynchronously await a stable state. The synchronous section consists of all the remaining steps of this algorithm until the algorithm says the synchronous section has ended. (Steps in synchronous sections are marked with ⌛.)
12. ⌛ Forget the media element's media-resource-specific text tracks.
13. ⌛ Find next candidate: Let candidate be null.
14. ⌛ Search loop: If the node after pointer is the end of the list, then jump to the waiting step below.
15. ⌛ If the node after pointer is a source element, let candidate be that element.
16. ⌛ Advance pointer so that the node before pointer is now the node that was after pointer, and the node after pointer is the node after the node that used to be after pointer, if any.
17. ⌛ If candidate is null, jump back to the search loop step. Otherwise, jump back to the process candidate step.
18. ⌛ Waiting: Set the element's networkState attribute to the NETWORK_NO_SOURCE value.
19. ⌛ Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
20. End the synchronous section, continuing the remaining steps asynchronously.
21. Wait until the node after pointer is a node other than the end of the list. (This step might wait forever.)
22. Asynchronously await a stable state. The synchronous section consists of all the remaining steps of this algorithm until the algorithm says the synchronous section has ended. (Steps in synchronous sections are marked with ⌛.)
23. ⌛ Set the element's delaying-the-load-event flag back to true (this delays the load event again, in case it hasn't been fired yet).
24. ⌛ Set the networkState back to NETWORK_LOADING.
25. ⌛ Jump back to the find next candidate step above.

The resource fetch algorithm for a media element and a given absolute URL is as follows:

Let the current media resource be the resource given by the absolute URL passed to this algorithm. This is now the element's media resource.
Begin to fetch the current media resource, from the media element's Document's origin, with the force same-origin flag set.

Every 350ms (±200ms) or for every byte received, whichever is least frequent, queue a task to fire a simple event named progress at the element.

The stall timeout is a user-agent defined length of time, which should be about three seconds. When a media element that is actively attempting to obtain media data has failed to receive any data for a duration equal to the stall timeout, the user agent must queue a task to fire a simple event named stalled at the element.

User agents may allow users to selectively block or slow media data downloads. When a media element's download has been blocked altogether, the user agent must act as if it was stalled (as opposed to acting as if the connection was closed). The rate of the download may also be throttled automatically by the user agent, e.g. to balance the download with other connections sharing the same bandwidth.

User agents may decide to not download more content at any time, e.g. after buffering five minutes of a one hour media resource, while waiting for the user to decide whether to play the resource or not, or while waiting for user input in an interactive resource. When a media element's download has been suspended, the user agent must set the networkState to NETWORK_IDLE and queue a task to fire a simple event named suspend at the element. If and when downloading of the resource resumes, the user agent must set the networkState to NETWORK_LOADING.

The preload attribute provides a hint regarding how much buffering the author thinks is advisable, even in the absence of the autoplay attribute.

When a user agent decides to completely stall a download, e.g. if it is waiting until the user starts playback before downloading any further content, the element's delaying-the-load-event flag must be set to false. This stops delaying the load event.

The user agent may use whatever means necessary to fetch the resource (within the constraints put forward by this and other specifications); for example, reconnecting to the server in the face of network errors, using HTTP range retrieval requests, or switching to a streaming protocol. The user agent must consider a resource erroneous only if it has given up trying to fetch it.

The networking task source tasks to process the data as it is being fetched must, when appropriate, include the relevant substeps from the following list:
If the media data cannot be fetched at all, due to network errors, causing the user agent to give up trying to fetch the resource

If the media resource is found to have Content-Type metadata that, when parsed as a MIME type (including any codecs described by the codecs parameter, if the parameter is defined for that type), represents a type that the user agent knows it cannot render (even if the actual media data is in a supported format)

If the media data can be fetched but is found by inspection to be in an unsupported format, or can otherwise not be rendered at all
DNS errors, HTTP 4xx and 5xx errors (and equivalents in other protocols), and other fatal network errors that occur before the user agent has established whether the current media resource is usable, as well as the file using an unsupported container format, or using unsupported codecs for all the data, must cause the user agent to execute the following steps:
1. The user agent should cancel the fetching process.
2. Abort this subalgorithm, returning to the resource selection algorithm.
Once enough of the media data has been fetched to determine the duration of the media resource, its dimensions, and other metadata, and once the text tracks are ready
This indicates that the resource is usable. The user agent must follow these substeps:
1. Establish the media timeline for the purposes of the current playback position, the earliest possible position, and the initial playback position, based on the media data.
2. Update the timeline offset to the date and time that corresponds to the zero time in the media timeline established in the previous step, if any. If no explicit time and date is given by the media resource, the timeline offset must be set to Not-a-Number (NaN).
3. Set the current playback position to the earliest possible position.
4. Update the duration attribute with the time of the last frame of the resource, if known, on the media timeline established above. If it is not known (e.g. a stream that is in principle infinite), update the duration attribute to the value positive Infinity.
  
  The user agent will queue a task to fire a simple event named durationchange at the element at this point.
5. For video elements, set the videoWidth and videoHeight attributes.
6. Set the readyState attribute to HAVE_METADATA.
  
  A loadedmetadata DOM event will be fired as part of setting the readyState attribute to a new value.
7. Let jumped be false.
8. If either the media resource or the address of the current media resource indicate a particular start time, then set the initial playback position to that time, seek to that time, and let jumped be true. Ignore any resulting exceptions (if the position is out of range, it is effectively ignored).
  
  For example, with media formats that support the Media Fragments URI fragment identifier syntax, the fragment identifier can be used to indicate a start position. [MEDIAFRAG]
9. If either the media resource or the address of the current media resource indicate a particular set of audio or video tracks to enable, then the selected audio tracks must be enabled in the element's audioTracks object, and the first selected video track must be selected in the element's videoTracks object.
10. If the media element has a current media controller, then: if jumped is true and the initial playback position, relative to the current media controller's timeline, is greater than the current media controller's media controller position, then seek the media controller to the media element's initial playback position, relative to the current media controller's timeline; otherwise, seek the media element to the media controller position, relative to the media element's timeline, discarding any resulting exceptions.
11. Once the readyState attribute reaches HAVE_CURRENT_DATA, after the loadeddata event has been fired, set the element's delaying-the-load-event flag to false. This stops delaying the load event.
  
  A user agent that is attempting to reduce network usage while still fetching the metadata for each media resource would also stop buffering at this point, causing the networkState attribute to switch to the NETWORK_IDLE value.
The user agent is required to determine the duration of the media resource and go through this step before playing.
Once the entire media resource has been fetched (but potentially before any of it has been decoded)

Queue a task to fire a simple event named progress at the media element.

If the connection is interrupted, causing the user agent to give up trying to fetch the resource
Fatal network errors that occur after the user agent has established whether the current media resource is usable must cause the user agent to execute the following steps:
1. The user agent should cancel the fetching process.
2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_NETWORK.
3. Queue a task to fire a simple event named error at the media element.
4. If the media element's readyState attribute has a value equal to HAVE_NOTHING, set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event named emptied at the element. Otherwise, set the element's networkState attribute to the NETWORK_IDLE value.
5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
6. Abort the overall resource selection algorithm.
If the media data is corrupted
Fatal errors in decoding the media data that occur after the user agent has established whether the current media resource is usable must cause the user agent to execute the following steps:
1. The user agent should cancel the fetching process.
2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_DECODE.
3. Queue a task to fire a simple event named error at the media element.
4. If the media element's readyState attribute has a value equal to HAVE_NOTHING, set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event named emptied at the element. Otherwise, set the element's networkState attribute to the NETWORK_IDLE value.
5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
6. Abort the overall resource selection algorithm.
If the media data fetching process is aborted by the user
The fetching process is aborted by the user, e.g. because the user navigated the browsing context to another page, the user agent must execute the following steps. These steps are not followed if the load() method itself is invoked while these steps are running, as the steps above handle that particular kind of abort.
1. The user agent should cancel the fetching process.
2. Set the error attribute to a new MediaError object whose code attribute is set to MEDIA_ERR_ABORTED.
3. Queue a task to fire a simple event named abort at the media element.
4. If the media element's readyState attribute has a value equal to HAVE_NOTHING, set the element's networkState attribute to the NETWORK_EMPTY value and queue a task to fire a simple event named emptied at the element. Otherwise, set the element's networkState attribute to the NETWORK_IDLE value.
5. Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
6. Abort the overall resource selection algorithm.
If the media data can be fetched but has non-fatal errors or uses, in part, codecs that are unsupported, preventing the user agent from rendering the content completely correctly but not preventing playback altogether

The server returning data that is partially usable but cannot be optimally rendered must cause the user agent to render just the bits it can handle, and ignore the rest.

If the media resource is found to declare a media-resource-specific text track that the user agent supports

If the media resource's origin is the same origin as the media element's Document's origin, queue a task to run the steps to expose a media-resource-specific text track with the relevant data.

Cross-origin files do not expose their subtitles in the DOM, for security reasons. However, user agents may still provide the user with access to such data in their user interface.
When the networking task source has queued the last task as part of fetching the media resource (i.e. once the download has completed), if the fetching process completes without errors, including decoding the media data, and if all of the data is available to the user agent without network access, then, the user agent must move on to the next step. This might never happen, e.g. when streaming an infinite resource such as Web radio, or if the resource is longer than the user agent's ability to cache data.

While the user agent might still need network access to obtain parts of the media resource, the user agent must remain on this step.

For example, if the user agent has discarded the first half of a video, the user agent will remain at this step even once the playback has ended, because there is always the chance the user will seek back to the start. In fact, in this situation, once playback has ended, the user agent will end up dispatching a stalled event, as described earlier.
If the user agent ever reaches this step (which can only happen if the entire resource gets loaded and kept available): abort the overall resource selection algorithm.

The preload attribute is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.

Keyword	State	Brief description
`none`	None	Hints to the user agent that either the author does not expect the user to need the media resource, or that the server wants to minimise unnecessary traffic.
`metadata`	Metadata	Hints to the user agent that the author does not expect the user to need the media resource, but that fetching the resource metadata (dimensions, first frame, track list, duration, etc) is reasonable.
`auto`	Automatic	Hints to the user agent that the user agent can put the user's needs first without risk to the server, up to and including optimistically downloading the entire resource.

The empty string is also a valid keyword, and maps to the Automatic state. The attribute's missing value default is user-agent defined, though the Metadata state is suggested as a compromise between reducing server load and providing an optimal user experience.

The preload attribute is intended to provide a hint to the user agent about what the author thinks will lead to the best user experience. The attribute may be ignored altogether, for example based on explicit user preferences or based on the available connectivity.

The preload IDL attribute must reflect the content attribute of the same name, limited to only known values.

The autoplay attribute can override the preload attribute (since if the media plays, it naturally has to buffer first, regardless of the hint given by the preload attribute). Including both is not an error, however.

media . buffered: Returns a TimeRanges object that represents the ranges of the media resource that the user agent has buffered.

The buffered attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has buffered, at the time the attribute is evaluated. Users agents must accurately determine the ranges available, even for media streams where this can only be determined by tedious inspection.

Typically this will be a single range anchored at the zero point, but if, e.g. the user agent uses HTTP range requests in response to seeking, then there could be multiple ranges.

User agents may discard previously buffered data.

Thus, a time position included within a range of the objects return by the buffered attribute at one time can end up being not included in the range(s) of objects returned by the same attribute at later times.

4.8.10.6 Offsets into the media resource

media . duration

Returns the length of the media resource, in seconds, assuming that the start of the media resource is at time zero.

Returns NaN if the duration isn't available.

Returns Infinity for unbounded streams.

media . currentTime [ = value ]

Returns the current playback position, in seconds.

Can be set, to seek to the given time.

Will throw an INVALID_STATE_ERR exception if there is no selected media resource or if there is a current media controller. Will throw an INDEX_SIZE_ERR exception if the given time is not within the ranges to which the user agent can seek.

media . initialTime

Returns the initial playback position, that is, time to which the media resource was automatically seeked when it was loaded. Returns zero if the initial playback position is still unknown.

A media resource has a media timeline that maps times (in seconds) to positions in the media resource. The origin of a timeline is its earliest defined position. The duration of a timeline is its last defined position.

Establishing the media timeline: If the media resource somehow specifies an explicit timeline whose origin is not negative, then the media timeline should be that timeline. (Whether the media resource can specify a timeline or not depends on the media resource's format.) If the media resource specifies an explicit start time and date, then that time and date should be considered the zero point in the media timeline; the timeline offset will be the time and date, exposed using the startOffsetTime attribute.

If the media resource has a discontinuous timeline, the user agent must extend the timeline used at the start of the resource across the entire resource, so that the media timeline of the media resource increases linearly starting from the earliest possible position (as defined below), even if the underlying media data has out-of-order or even overlapping time codes.

For example, if two clips have been concatenated into one video file, but the video format exposes the original times for the two clips, the video data might expose a timeline that goes, say, 00:15..00:29 and then 00:05..00:38. However, the user agent would not expose those times; it would instead expose the times as 00:15..00:29 and 00:29..01:02, as a single video.

In the absence of an explicit timeline, the zero time on the media timeline should correspond to the first frame of the media resource. For static audio and video files this is generally trivial. For streaming resources, if the user agent will be able to seek to an earlier point than the first frame originally provided by the server, then the zero time should correspond to the earliest seekable time of the media resource; otherwise, it should correspond to the first frame received from the server (the point in the media resource at which the user agent began receiving the stream).

Another example would be a stream that carries a video with several concatenated fragments, broadcast by a server that does not allow user agents to request specific times but instead just streams the video data in a predetermined order. If a user agent connects to this stream and receives fragments defined as covering timestamps 2010-03-20 23:15:00 UTC to 2010-03-21 00:05:00 UTC and 2010-02-12 14:25:00 UTC to 2010-02-12 14:35:00 UTC, it would expose this with a media timeline starting at 0s and extending to 3,600s (one hour). Assuming the streaming server disconnected at the end of the second clip, the duration attribute would then return 3,600. The startOffsetTime attribute would return a Date object with a time corresponding to 2010-03-20 23:15:00 UTC. However, if a different user agent connected five minutes later, it would (presumably) receive fragments covering timestamps 2010-03-20 23:20:00 UTC to 2010-03-21 00:05:00 UTC and 2010-02-12 14:25:00 UTC to 2010-02-12 14:35:00 UTC, and would expose this with a media timeline starting at 0s and extending to 3,300s (fifty five minutes). In this case, the startOffsetTime attribute would return a Date object with a time corresponding to 2010-03-20 23:20:00 UTC.

In any case, the user agent must ensure that the earliest possible position (as defined below) using the established media timeline, is greater than or equal to zero.

The media timeline also has an associated clock. Which clock is used is user-agent defined, and may be media resource-dependent, but it should approximate the user's wall clock.

All the media elements that share current media controller use the same clock for their media timeline.

Media elements have a current playback position, which must initially (i.e. in the absence of media data) be zero seconds. The current playback position is a time on the media timeline.

The currentTime attribute must, on getting, return the current playback position, expressed in seconds. On setting, if the media element has a current media controller, then it must throw an INVALID_STATE_ERR exception; otherwise, the user agent must seek to the new value (which might raise an exception).

Media elements have an initial playback position, which must initially (i.e. in the absence of media data) be zero seconds. The initial playback position is updated when a media resource is loaded. The initial playback position is a time on the media timeline.

The initialTime attribute must, on getting, return the initial playback position, expressed in seconds.

If the media resource is a streaming resource, then the user agent might be unable to obtain certain parts of the resource after it has expired from its buffer. Similarly, some media resources might have a media timeline that doesn't start at zero. The earliest possible position is the earliest position in the stream or resource that the user agent can ever obtain again. It is also a time on the media timeline.

The earliest possible position is not explicitly exposed in the API; it corresponds to the start time of the first range in the seekable attribute's TimeRanges object, if any, or the current playback position otherwise.

When the earliest possible position changes, then: if the current playback position is before the earliest possible position, the user agent must seek to the earliest possible position; otherwise, if the user agent has not fired a timeupdate event at the element in the past 15 to 250ms and is not still running event handlers for such an event, then the user agent must queue a task to fire a simple event named timeupdate at the element.

Because of the above requirement and the requirement in the resource fetch algorithm that kicks in when the metadata of the clip becomes known, the current playback position can never be less than the earliest possible position.

The duration attribute must return the time of the end of the media resource, in seconds, on the media timeline. If no media data is available, then the attributes must return the Not-a-Number (NaN) value. If the media resource is known to be unbounded (e.g. a streaming radio), then the attribute must return the positive Infinity value.

The user agent must determine the duration of the media resource before playing any part of the media data and before setting readyState to a value equal to or greater than HAVE_METADATA, even if doing so requires fetching multiple parts of the resource.

When the length of the media resource changes to a known value (e.g. from being unknown to known, or from a previously established length to a new length) the user agent must queue a task to fire a simple event named durationchange at the media element. (The event is not fired when the duration is reset as part of loading a new media resource.)

If an "infinite" stream ends for some reason, then the duration would change from positive Infinity to the time of the last frame or sample in the stream, and the durationchange event would be fired. Similarly, if the user agent initially estimated the media resource's duration instead of determining it precisely, and later revises the estimate based on new information, then the duration would change and the durationchange event would be fired.

Some video files also have an explicit date and time corresponding to the zero time in the media timeline, known as the timeline offset. Initially, the timeline offset must be set to Not-a-Number (NaN).

The startOffsetTime attribute must return a new Date object representing the current timeline offset.

The loop attribute is a boolean attribute that, if specified, indicates that the media element is to seek back to the start of the media resource upon reaching the end.

The loop attribute has no effect while the element has a current media controller.

The loop IDL attribute must reflect the content attribute of the same name.

4.8.10.7 The ready states

media . readyState: Returns a value that expresses the current state of the element with respect to rendering the current playback position, from the codes in the list below.

Media elements have a ready state, which describes to what degree they are ready to be rendered at the current playback position. The possible values are as follows; the ready state of a media element at any particular time is the greatest value describing the state of the element:

HAVE_NOTHING (numeric value 0): No information regarding the media resource is available. No data for the current playback position is available. Media elements whose networkState attribute are set to NETWORK_EMPTY are always in the HAVE_NOTHING state.
HAVE_METADATA (numeric value 1): Enough of the resource has been obtained that the duration of the resource is available. In the case of a video element, the dimensions of the video are also available. The API will no longer raise an exception when seeking. No media data is available for the immediate current playback position. The text tracks are ready.
HAVE_CURRENT_DATA (numeric value 2): Data for the immediate current playback position is available, but either not enough data is available that the user agent could successfully advance the current playback position in the direction of playback at all without immediately reverting to the HAVE_METADATA state, or there is no more data to obtain in the direction of playback. For example, in video this corresponds to the user agent having data from the current frame, but not the next frame; and to when playback has ended.
HAVE_FUTURE_DATA (numeric value 3): Data for the immediate current playback position is available, as well as enough data for the user agent to advance the current playback position in the direction of playback at least a little without immediately reverting to the HAVE_METADATA state. For example, in video this corresponds to the user agent having data for at least the current frame and the next frame. The user agent cannot be in this state if playback has ended, as the current playback position can never advance in this case.
HAVE_ENOUGH_DATA (numeric value 4): All the conditions described for the HAVE_FUTURE_DATA state are met, and, in addition, the user agent estimates that data is being fetched at a rate where the current playback position, if it were to advance at the effective playback rate, would not overtake the available data before playback reaches the end of the media resource.

When the ready state of a media element whose networkState is not NETWORK_EMPTY changes, the user agent must follow the steps given below:

Apply the first applicable set of substeps from the following list:

If the previous ready state was HAVE_NOTHING, and the new ready state is HAVE_METADATA

Queue a task to fire a simple event named loadedmetadata at the element.

Before this task is run, as part of the event loop mechanism, the rendering will have been updated to resize the video element if appropriate.

If the previous ready state was HAVE_METADATA and the new ready state is HAVE_CURRENT_DATA or greater

If this is the first time this occurs for this media element since the load() algorithm was last invoked, the user agent must queue a task to fire a simple event named loadeddata at the element.

If the new ready state is HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA, then the relevant steps below must then be run also.

If the previous ready state was HAVE_FUTURE_DATA or more, and the new ready state is HAVE_CURRENT_DATA or less

If the media element was potentially playing before its readyState attribute changed to a value lower than HAVE_FUTURE_DATA, and the element has not ended playback, and playback has not stopped due to errors, and playback has not paused for user interaction, the user agent must queue a task to fire a simple event named timeupdate at the element, and queue a task to fire a simple event named waiting at the element.

If the previous ready state was HAVE_CURRENT_DATA or less, and the new ready state is HAVE_FUTURE_DATA

The user agent must queue a task to fire a simple event named canplay.

If the element's paused attribute is false, the user agent must queue a task to fire a simple event named playing.

If the new ready state is HAVE_ENOUGH_DATA

If the previous ready state was HAVE_CURRENT_DATA or less, the user agent must queue a task to fire a simple event named canplay, and, if the element's paused attribute is false, queue a task to fire a simple event named playing.

If the autoplaying flag is true, and the paused attribute is true, and the media element has an autoplay attribute specified, and the media element's Document's browsing context did not have the sandboxed automatic features browsing context flag set when the Document was created, then the user agent may also set the paused attribute to false, queue a task to fire a simple event named play, and queue a task to fire a simple event named playing.

User agents do not need to support autoplay, and it is suggested that user agents honor user preferences on the matter. Authors are urged to use the autoplay attribute rather than using script to force the video to play, so as to allow the user to override the behavior if so desired.

In any case, the user agent must finally queue a task to fire a simple event named canplaythrough.
If the media element has a current media controller, then report the controller state for the media element's current media controller.

It is possible for the ready state of a media element to jump between these states discontinuously. For example, the state of a media element can jump straight from HAVE_METADATA to HAVE_ENOUGH_DATA without passing through the HAVE_CURRENT_DATA and HAVE_FUTURE_DATA states.

The readyState IDL attribute must, on getting, return the value described above that describes the current ready state of the media element.

The autoplay attribute is a boolean attribute. When present, the user agent (as described in the algorithm described herein) will automatically begin playback of the media resource as soon as it can do so without stopping.

Authors are urged to use the autoplay attribute rather than using script to trigger automatic playback, as this allows the user to override the automatic playback when it is not desired, e.g. when using a screen reader. Authors are also encouraged to consider not using the automatic playback behavior at all, and instead to let the user agent wait for the user to start playback explicitly.

The autoplay IDL attribute must reflect the content attribute of the same name.

4.8.10.8 Playing the media resource

media . paused

Returns true if playback is paused; false otherwise.

media . ended

Returns true if playback has reached the end of the media resource.

media . defaultPlaybackRate [ = value ]

Returns the default rate of playback, for when the user is not fast-forwarding or reversing through the media resource.

Can be set, to change the default rate of playback.

The default rate has no direct effect on playback, but if the user switches to a fast-forward mode, when they return to the normal playback mode, it is expected that the rate of playback will be returned to the default rate of playback.

When the element has a current media controller, the defaultPlaybackRate attribute is ignored and the current media controller's defaultPlaybackRate is used instead.

media . playbackRate [ = value ]

Returns the current rate playback, where 1.0 is normal speed.

Can be set, to change the rate of playback.

When the element has a current media controller, the playbackRate attribute is ignored and the current media controller's playbackRate is used instead.

media . played

Returns a TimeRanges object that represents the ranges of the media resource that the user agent has played.

media . play()

Sets the paused attribute to false, loading the media resource and beginning playback if necessary. If the playback had ended, will restart it from the start.

media . pause()

Sets the paused attribute to true, loading the media resource if necessary.

The paused attribute represents whether the media element is paused or not. The attribute must initially be true.

A media element is a blocked media element if its readyState attribute is in the HAVE_NOTHING state or the HAVE_METADATA state, or if the element has paused for user interaction.

A media element is said to be potentially playing when its paused attribute is false, the element has not ended playback, playback has not stopped due to errors, the element either has no current media controller or has a current media controller but is not blocked on its media controller, and the element is not a blocked media element.

A media element is said to have ended playback when:

The element's readyState attribute is HAVE_METADATA or greater, and
Either:
- The current playback position is the end of the media resource, and
- The direction of playback is forwards, and
- Either the media element does not have a loop attribute specified, or the media element has a current media controller.
Or:
- The current playback position is the earliest possible position, and
- The direction of playback is backwards.

The ended attribute must return true if the media element has ended playback and the direction of playback is forwards, and false otherwise.

A media element is said to have stopped due to errors when the element's readyState attribute is HAVE_METADATA or greater, and the user agent encounters a non-fatal error during the processing of the media data, and due to that error, is not able to play the content at the current playback position.

A media element is said to have paused for user interaction when its paused attribute is false, the readyState attribute is either HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA and the user agent has reached a point in the media resource where the user has to make a selection for the resource to continue. If the media element has a current media controller when this happens, then the user agent must report the controller state for the media element's current media controller. If If the media element has a current media controller when the user makes a selection, allowing playback to resume, the user agent must similarly report the controller state for the media element's current media controller.

It is possible for a media element to have both ended playback and paused for user interaction at the same time.

When a media element that is potentially playing stops playing because it has paused for user interaction, the user agent must queue a task to fire a simple event named timeupdate at the element.

A waiting DOM event can be fired as a result of an element that is potentially playing stopping playback due to its readyState attribute changing to a value lower than HAVE_FUTURE_DATA.

When the current playback position reaches the end of the media resource when the direction of playback is forwards, then the user agent must follow these steps:

If the media element has a loop attribute specified and does not have a current media controller, then seek to the earliest possible position of the media resource and abort these steps.
Stop playback.
The ended attribute becomes true.
The user agent must queue a task to fire a simple event named timeupdate at the element.
The user agent must queue a task to fire a simple event named ended at the element.

When the current playback position reaches the earliest possible position of the media resource when the direction of playback is backwards, then the user agent must follow these steps:

Stop playback.
The user agent must queue a task to fire a simple event named timeupdate at the element.

The defaultPlaybackRate attribute gives the desired speed at which the media resource is to play, as a multiple of its intrinsic speed. The attribute is mutable: on getting it must return the last value it was set to, or 1.0 if it hasn't yet been set; on setting the attribute must be set to the new value.

The defaultPlaybackRate is used by the user agent when it exposes a user interface to the user.

The playbackRate attribute gives the effective playback rate (assuming there is no current media controller overriding it), which is the speed at which the media resource plays, as a multiple of its intrinsic speed. If it is not equal to the defaultPlaybackRate, then the implication is that the user is using a feature such as fast forward or slow motion playback. The attribute is mutable: on getting it must return the last value it was set to, or 1.0 if it hasn't yet been set; on setting the attribute must be set to the new value, and the playback will change speed (if the element is potentially playing and there is no current media controller).

When the defaultPlaybackRate or playbackRate attributes change value (either by being set by script or by being changed directly by the user agent, e.g. in response to user control) the user agent must queue a task to fire a simple event named ratechange at the media element.

The defaultPlaybackRate and playbackRate attributes have no effect when the media element has a current media controller; the namesake attributes on the MediaController object are used instead in that situation.

The played attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has so far rendered, at the time the attribute is evaluated.

When the play() method on a media element is invoked, the user agent must run the following steps.

If the media element's networkState attribute has the value NETWORK_EMPTY, invoke the media element's resource selection algorithm.
If the playback has ended and the direction of playback is forwards, and the media element does not have a current media controller, seek to the earliest possible position of the media resource.

This will cause the user agent to queue a task to fire a simple event named timeupdate at the media element.
If the media element has a current media controller, then bring the media element up to speed with its new media controller.
If the media element's paused attribute is true, run the following substeps:
1. Change the value of paused to false.
2. Queue a task to fire a simple event named play at the element.
3. If the media element's readyState attribute has the value HAVE_NOTHING, HAVE_METADATA, or HAVE_CURRENT_DATA, queue a task to fire a simple event named waiting at the element.
  
  Otherwise, the media element's readyState attribute has the value HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA: queue a task to fire a simple event named playing at the element.
Set the media element's autoplaying flag to false.
If the media element has a current media controller, then report the controller state for the media element's current media controller.

When the pause() method is invoked, and when the user agent is required to pause the media element, the user agent must run the following steps:

If the media element's networkState attribute has the value NETWORK_EMPTY, invoke the media element's resource selection algorithm.
Set the media element's autoplaying flag to false.
If the media element's paused attribute is false, run the following steps:
1. Change the value of paused to true.
2. Queue a task to fire a simple event named timeupdate at the element.
3. Queue a task to fire a simple event named pause at the element.
If the media element has a current media controller, then report the controller state for the media element's current media controller.

The effective playback rate is not necessarily the element's playbackRate. When a media element has a current media controller, its effective playback rate is the MediaController's media controller playback rate. Otherwise, the effective playback rate is just the element's playbackRate. Thus, the current media controller overrides the media element.

If the effective playback rate is positive or zero, then the direction of playback is forwards. Otherwise, it is backwards.

When a media element is potentially playing and its Document is a fully active Document, its current playback position must increase monotonically at effective playback rate units of media time per unit time of the media timeline's clock.

The effective playback rate can be 0.0, in which case the current playback position doesn't move, despite playback not being paused (paused doesn't become true, and the pause event doesn't fire).

This specification doesn't define how the user agent achieves the appropriate playback rate — depending on the protocol and media available, it is plausible that the user agent could negotiate with the server to have the server provide the media data at the appropriate rate, so that (except for the period between when the rate is changed and when the server updates the stream's playback rate) the client doesn't actually have to drop or interpolate any frames.

When the direction of playback is backwards, any corresponding audio must be muted. When the effective playback rate is so low or so high that the user agent cannot play audio usefully, the corresponding audio must also be muted. If the effective playback rate is not 1.0, the user agent may apply pitch adjustments to the audio as necessary to render it faithfully.

Media elements that are potentially playing while not in a Document must not play any video, but should play any audio component. Media elements must not stop playing just because all references to them have been removed; only once a media element is in a state where no further audio could ever be played by that element may the element be garbage collected.

It is possible for an element to which no explicit references exist to play audio, even if such an element is not still actively playing: for instance, it could have a current media controller that still has references and can still be unpaused, or it could be unpaused but stalled waiting for content to buffer.

When the current playback position of a media element changes (e.g. due to playback or seeking), the user agent must run the following steps. If the current playback position changes while the steps are running, then the user agent must wait for the steps to complete, and then must immediately rerun the steps. (These steps are thus run as often as possible or needed — if one iteration takes a long time, this can cause certain cues to be skipped over as the user agent rushes ahead to "catch up".)

Let current cues be an ordered list of cues, initialized to contain all the cues of all the hidden, showing, or showing by default text tracks of the media element (not the disabled ones) whose start times are less than or equal to the current playback position and whose end times are greater than the current playback position, in text track cue order.
Let other cues be an ordered list of cues, initialized to contain all the cues of hidden, showing, and showing by default text tracks of the media element that are not present in current cues, also in text track cue order.
If the time was reached through the usual monotonic increase of the current playback position during normal playback, and if the user agent has not fired a timeupdate event at the element in the past 15 to 250ms and is not still running event handlers for such an event, then the user agent must queue a task to fire a simple event named timeupdate at the element. (In the other cases, such as explicit seeks, relevant events get fired as part of the overall process of changing the current playback position.)

The event thus is not to be fired faster than about 66Hz or slower than 4Hz (assuming the event handlers don't take longer than 250ms to run). User agents are encouraged to vary the frequency of the event based on the system load and the average cost of processing the event each time, so that the UI updates are not any more frequent than the user agent can comfortably handle while decoding the video.
If all of the cues in current cues have their text track cue active flag set, and none of the cues in other cues have their text track cue active flag set, then abort these steps.
If the time was reached through the usual monotonic increase of the current playback position during normal playback, and there are cues in other cues that have both their text track cue active flag set and their text track cue pause-on-exit flag set, then immediately pause the media element. (In the other cases, such as explicit seeks, playback is not paused by going past the end time of a cue, even if that cue has its text track cue pause-on-exit flag set.)
Let affected tracks be a list of text tracks, initially empty.
For each text track cue in other cues that has its text track cue active flag set, in list order, queue a task to fire a simple event named exit at the TextTrackCue object, and add the cue's text track to affected tracks, if it's not already in the list.
For each text track cue in current cues that does not have its text track cue active flag set, in list order, queue a task to fire a simple event named enter at the TextTrackCue object, and add the cue's text track to affected tracks, if it's not already in the list.
For each text track in affected tracks, in the order they were added to the list (which will match the relative order of the text tracks in the media element's list of text tracks), queue a task to fire a simple event named cuechange at the TextTrack object, and, if the text track has a corresponding track element, to then fire a simple event named cuechange at the track element as well.
Set the text track cue active flag of all the cues in the current cues, and unset the text track cue active flag of all the cues in the other cues.
Run the rules for updating the text track rendering of each of the text tracks in affected tracks that are showing or showing by default.

For the purposes of the algorithm above, a text track cue is considered to be part of a text track only if it is listed in the text track list of cues, not merely if it is associated with the text track.

If the media element's Document stops being a fully active document, then the playback will stop until the document is active again.

When a media element is removed from a Document, the user agent must run the following steps:

Asynchronously await a stable state, allowing the task that removed the media element from the Document to continue. The synchronous section consists of all the remaining steps of this algorithm. (Steps in the synchronous section are marked with ⌛.)
⌛ If the media element is in a Document, abort these steps.
⌛ If the media element's networkState attribute has the value NETWORK_EMPTY, abort these steps.
⌛ Pause the media element.

4.8.10.9 Seeking

media . seeking: Returns true if the user agent is currently seeking.
media . seekable: Returns a TimeRanges object that represents the ranges of the media resource to which it is possible for the user agent to seek.

The seeking attribute must initially have the value false.

When the user agent is required to seek to a particular new playback position in the media resource, it means that the user agent must run the following steps. This algorithm interacts closely with the event loop mechanism; in particular, it has a synchronous section (which is triggered as part of the event loop algorithm). Steps in that section are marked with ⌛.

If the media element's readyState is HAVE_NOTHING, then raise an INVALID_STATE_ERR exception (if the seek was in response to a DOM method call or setting of an IDL attribute), and abort these steps.
If the element's seeking IDL attribute is true, then another instance of this algorithm is already running. Abort that other instance of the algorithm without waiting for the step that it is running to complete.
Set the seeking IDL attribute to true.
If the seek was in response to a DOM method call or setting of an IDL attribute, then continue the script. The remainder of these steps must be run asynchronously. With the exception of the steps marked with ⌛, they could be aborted at any time by another instance of this algorithm being invoked.
If the new playback position is later than the end of the media resource, then let it be the end of the media resource instead.
If the new playback position is less than the earliest possible position, let it be that position instead.
If the (possibly now changed) new playback position is not in one of the ranges given in the seekable attribute, then let it be the position in one of the ranges given in the seekable attribute that is the nearest to the new playback position. If two positions both satisfy that constraint (i.e. the new playback position is exactly in the middle between two ranges in the seekable attribute) then use the position that is closest to the current playback position. If there are no ranges given in the seekable attribute then set the seeking IDL attribute to false and abort these steps.
Queue a task to fire a simple event named seeking at the element.
Set the current playback position to the given new playback position.

If the media element was potentially playing immediately before it started seeking, but seeking caused its readyState attribute to change to a value lower than HAVE_FUTURE_DATA, then a waiting will be fired at the element.
Wait until the user agent has established whether or not the media data for the new playback position is available, and, if it is, until it has decoded enough data to play back that position.
Await a stable state. The synchronous section consists of all the remaining steps of this algorithm. (Steps in the synchronous section are marked with ⌛.)
⌛ Set the seeking IDL attribute to false.
Queue a task to fire a simple event named timeupdate at the element.
⌛ Queue a task to fire a simple event named seeked at the element.

The seekable attribute must return a new static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent is able to seek to, at the time the attribute is evaluated.

If the user agent can seek to anywhere in the media resource, e.g. because it is a simple movie file and the user agent and the server support HTTP Range requests, then the attribute would return an object with one range, whose start is the time of the first frame (the earliest possible position, typically zero), and whose end is the same as the time of the first frame plus the duration attribute's value (which would equal the time of the last frame, and might be positive Infinity).

The range might be continuously changing, e.g. if the user agent is buffering a sliding window on an infinite stream. This is the behavior seen with DVRs viewing live TV, for instance.

Media resources might be internally scripted or interactive. Thus, a media element could play in a non-linear fashion. If this happens, the user agent must act as if the algorithm for seeking was used whenever the current playback position changes in a discontinuous fashion (so that the relevant events fire). If the media element has a current media controller, then the user agent must seek the media controller appropriately instead.

4.8.10.10 Media resources with multiple media tracks

A media resource can have multiple embedded audio and video tracks. For example, in addition to the primary video and audio tracks, a media resource could have foreign-language dubbed dialogues, director's commentaries, audio descriptions, alternative angles, or sign-language overlays.

media . audioTracks: Returns a MultipleTrackList object representing the audio tracks available in the media resource.
media . videoTracks: Returns an ExclusiveTrackList object representing the video tracks available in the media resource.

The audioTracks attribute of a media element must return a live MultipleTrackList object representing the audio tracks available in the media element's media resource. The same object must be returned each time.

The videoTracks attribute of a media element must return a live ExclusiveTrackList object representing the video tracks available in the media element's media resource. The same object must be returned each time.

There are only ever two TrackList objects (one MultipleTrackList object and one ExclusiveTrackList object) per media element, even if another media resource is loaded into the element: the objects are reused.

4.8.10.10.1 `TrackList` objects

The MultipleTrackList and ExclusiveTrackList interfaces, used by the attributes defined in the previous section, are substantially similar. Their common features are defined in the TrackList interface, from which they both inherit.

interface TrackList {
  readonly attribute unsigned long length;
  DOMString getID(in unsigned long index);
  DOMString getKind(in unsigned long index);
  DOMString getLabel(in unsigned long index);
  DOMString getLanguage(in unsigned long index);

           attribute Function onchange;
};

interface MultipleTrackList : TrackList {
  boolean isEnabled(in unsigned long index);
  void enable(in unsigned long index);
  void disable(in unsigned long index);
};

interface ExclusiveTrackList : TrackList {
  readonly attribute unsigned long selectedIndex;
  void select(in unsigned long index);
};

tracks . length: Returns the number of tracks in the list.
id = tracks . getID( index ): Returns the ID of the given track. This is the ID that can be used with a fragment identifier if the format supports the Media Fragments URI syntax. [MEDIAFRAG]
kind = tracks . getKind( index ): Returns the category the given track falls into. The possible track categories are given below.
label = tracks . getLabel( index ): Returns the label of the given track, if known, or the empty string otherwise.
language = tracks . getLanguage( index ): Returns the language of the given track, if known, or the empty string otherwise.
enabled = audioTracks . isEnabled( index ): Returns true if the given track is active, and false otherwise.
audioTracks . enable( index ): Enables the given track.
audioTracks . disable( index ): Disables the given track.
videoTracks . isEnabled: Returns the index of the currently selected track, if any, or −1 otherwise.
videoTracks . select( index ): Selects the given track.

The length attribute must return the number of tracks represented by the TrackList object at the time of getting.

Tracks in a TrackList object must be consistently ordered. If the media resource is in a format that defines an order, then that order must be used; otherwise, the order must be the relative order in which the tracks are declared in the media resource. Each track in a TrackList thus has an index; the first has the index 0, and each subsequent track is numbered one higher than the previous one.

The getID(index) method must return the identifier of the track with index index, if there is one. If there is no such track, then the method must instead throw an INDEX_SIZE_ERR exception. If the media resource is in a format that supports the Media Fragments URI fragment identifier syntax, the returned identifier must be the same identifier that would enable the track if used as the name of a track in the track dimension of such a fragment identifier. [MEDIAFRAG]

The getKind(index) method must return the category of the track with index index, if there is one. If there is no such track, then the method must instead throw an INDEX_SIZE_ERR exception.

The category of a track is the string given in the first column of the table below that is the most appropriate for the track based on the definitions in the table's second and third columns, as determined by the metadata included in the track in the media resource. For Ogg files, the Role header of the track gives the relevant metadata. The cell in the third column of a row says what the category given in the cell in the first column of that row applies to; a category is only appropriate for an audio track if it applies to audio tracks, and a category is only appropriate for video tracks if it applies to video tracks.

Return values for `getKind()`
Category	Definition	Applies to...	Examples
"`alternative`"	A possible alternative to the main track, e.g. a different take of a song (audio), or a different angle (video).	Audio and video.	Ogg: "audio/alterate" or "video/alternate".
"`description`"	An audio description of a video track.	Audio only.	Ogg: "audio/audiodesc".
"`main`"	The primary audio or video track.	Audio and video.	Ogg: "audio/main" or "video/main"; WebM: the "FlagDefault" element is set.
"`sign`"	A sign-language interpretation of an audio track.	Video only.	Ogg: "video/sign".
"`translation`"	A translated version of the main track.	Audio only.	Ogg: "audio/dub".
"" (empty string)	No explicit kind, or the kind given by the track's metadata is not recognised by the user agent.	Audio and video.	Any other track type or track role.

The getLabel(index) method must return the label of the track with index index, if there is one and it has a label. If there is no such track, then the method must instead throw an INDEX_SIZE_ERR exception. If there is a track with index index, but it has no label, then the method must return the empty string.

The getLanguage(index) method must return the BCP 47 language tag of the language of the track with index index, if there is one and it has a language. If there is no such track, then the method must instead throw an INDEX_SIZE_ERR exception. If there is a track with index index, but it has no language, or the user agent is not able to express that language as a BCP 47 language tag (for example because the language information in the media resource's format is a free-form string without a defined interpretation), then the method must return the empty string.

A MultipleTrackList object represents a track list where multiple tracks can be enabled simultaneously. Each track is either enabled or disabled.

The isEnabled(index) method must return true if there is a track with index index, and it is currently enabled, false if there is a track with index index, but it is currently disabled, and must throw an INDEX_SIZE_ERR exception if there is no track with index index.

The enable(index) method must enable the track with index index, if there is one. If there is not, it must instead throw an INDEX_SIZE_ERR exception.

The disable(index) method must disable the track with index index, if there is one. If there is not, it must instead throw an INDEX_SIZE_ERR exception.

Whenever a track is enabled or disabled, the user agent must queue a task to fire a simple event named change at the MultipleTrackList object.

An ExclusiveTrackList object represents a track list where exactly one track is selected at a time.

The selectedIndex attribute must return the index of the currently selected track. If the ExclusiveTrackList object does not represent any tracks, it must instead return −1.

The select(index) must select the track with index index, if there is one, unselecting whichever track was previously selected. If there is no track with index index, it must instead throw an INDEX_SIZE_ERR exception.

Whenever the selected track is changed, the user agent must queue a task to fire a simple event named change at the MultipleTrackList object.

The following are the event handlers (and their corresponding event handler event types) that must be supported, as IDL attributes, by all objects implementing the TrackList interface:

Event handler	Event handler event type
`onchange`	`change`

The task source for the tasks listed in this section is the DOM manipulation task source.

4.8.10.10.2 Selecting specific audio and video tracks declaratively

The audioTracks and videoTracks attributes allow scripts to select which track should play, but it is also possible to select specific tracks declaratively, by specifying particular tracks in the fragment identifier of the URL of the media resource. The format of the fragment identifier depends on the MIME type of the media resource. [RFC2046] [RFC3986]

In this example, a video that uses a format that supports the Media Fragments URI fragment identifier syntax is embedded in such a way that the alternative angles labeled "Alternative" are enabled instead of the default video track. [MEDIAFRAG]

<video src="myvideo#track=Alternative"></video>

4.8.10.11 Synchronising multiple media elements

4.8.10.11.1 Introduction

Each media element can have a MediaController. A MediaController is an object that coordinates the playback of multiple media elements, for instance so that a sign-language interpreter track can be overlaid on a video track, with the two being kept in sync.

By default, a media element has no MediaController. An implicit MediaController can be assigned using the mediagroup content attribute. An explicit MediaController can be assigned directly using the controller IDL attribute.

Media elements with a MediaController are said to be slaved to their controller. The MediaController modifies the playback rate and the playback volume of each of the media elements slaved to it, and ensures that when any of its slaved media elements unexpectedly stall, the others are stopped at the same time.

When a media element is slaved to a MediaController, its playback rate is fixed to that of the other tracks in the same MediaController, and any looping is disabled.

4.8.10.11.2 Media controllers

[Constructor]
interface MediaController {
  readonly attribute TimeRanges buffered;
  readonly attribute TimeRanges seekable;
  readonly attribute double duration;
           attribute double currentTime;

  readonly attribute boolean paused;
  readonly attribute TimeRanges played;
  void play();
  void pause();

           attribute double defaultPlaybackRate;
           attribute double playbackRate;

           attribute double volume;
           attribute boolean muted;

           attribute Function onemptied;
           attribute Function onloadedmetadata;
           attribute Function onloadeddata;
           attribute Function oncanplay;
           attribute Function oncanplaythrough;
           attribute Function onplaying;
           attribute Function onwaiting;

           attribute Function ondurationchange;
           attribute Function ontimeupdate;
           attribute Function onplay;
           attribute Function onpause;
           attribute Function onratechange;
           attribute Function onvolumechange;
};

controller = new MediaController()

Returns a new MediaController object.

media . controller [ = controller ]

Returns the current MediaController for the media element, if any; returns null otherwise.

Can be set, to set an explicit MediaController. Doing so removes the mediagroup attribute, if any.

controller . buffered

Returns a TimeRanges object that represents the intersection of the time ranges for which the user agent has all relevant media data for all the slaved media elements.

controller . seekable

Returns a TimeRanges object that represents the intersection of the time ranges into which the user agent can seek for all the slaved media elements.

controller . duration

Returns the difference between the earliest playable moment and the latest playable moment (not considering whether the data in question is actually buffered or directly seekable, but not including time in the future for infinite streams). Will return zero if there is no media.

controller . currentTime [ = value ]

Returns the current playback position, in seconds, as a position between zero time and the current duration.

Can be set, to seek to the given time.

controller . paused

Returns true if playback is paused; false otherwise. When this attribute is true, any media element slaved to this controller will be stopped.

controller . played

Returns a TimeRanges object that represents the union of the time ranges in all the slaved media elements that have been played.

controller . play()

Sets the paused attribute to false.

controller . pause()

Sets the paused attribute to true.

controller . defaultPlaybackRate [ = value ]

Returns the default rate of playback.

Can be set, to change the default rate of playback.

This default rate has no direct effect on playback, but if the user switches to a fast-forward mode, when they return to the normal playback mode, it is expected that rate of playback (playbackRate) will be returned to this default rate.

controller . playbackRate [ = value ]

Returns the current rate of playback.

Can be set, to change the rate of playback.

controller . volume [ = value ]

Returns the current playback volume multiplier, as a number in the range 0.0 to 1.0, where 0.0 is the quietest and 1.0 the loudest.

Can be set, to change the volume multiplier.

Throws an INDEX_SIZE_ERR if the new value is not in the range 0.0 .. 1.0.

controller . muted [ = value ]

Returns true if all audio is muted (regardless of other attributes either on the controller or on any media elements slaved to this controller), and false otherwise.

Can be set, to change whether the audio is muted or not.

A media element can have a current media controller, which is a MediaController object. When a media element is created without a mediagroup attribute, it does not have a current media controller. (If it is created with such an attribute, then that attribute initializes the current media controller, as defined below.)

The slaved media elements of a MediaController are the media elements whose current media controller is that MediaController. All the slaved media elements of a MediaController must use the same clock for their definition of their media timeline's unit time.

The controller attribute on a media element, on getting, must return the element's current media controller, if any, or null otherwise. On setting, it must first remove the element's mediagroup attribute, if any, and then set the current media controller to the given value. If the given value is null, the element no longer has a current media controller; if it is not null, then the user agent must bring the media element up to speed with its new media controller.

The MediaController() constructor, when invoked, must return a newly created MediaController object.

The seekable attribute must return a new static normalized TimeRanges object that represents the intersection of the ranges of the media resources of the slaved media elements that the user agent is able to seek to, at the time the attribute is evaluated.

The buffered attribute must return a new static normalized TimeRanges object that represents the intersection of the ranges of the media resources of the slaved media elements that the user agent has buffered, at the time the attribute is evaluated. Users agents must accurately determine the ranges available, even for media streams where this can only be determined by tedious inspection.

The duration attribute must return the media controller duration.

Every 15 to 250ms, or whenever the MediaController's media controller duration changes, whichever happens least often, the user agent must queue a task to fire a simple event named durationchange at the MediaController. If the MediaController's media controller duration decreases such that the media controller position is greater than the media controller duration, the user agent must immediately seek the media controller to media controller duration.

The currentTime attribute must return the media controller position on getting, and on setting must seek the media controller to the new value.

Every 15 to 250ms, or whenever the MediaController's media controller position changes, whichever happens least often, the user agent must queue a task to fire a simple event named timeupdate at the MediaController.

When a MediaController is created it is a playing media controller. It can be changed into a paused media controller and back either via the user agent's user interface (when the element is exposing a user interface to the user) or by script using the APIs defined in this section (see below).

The paused attribute must return true if the MediaController object is a paused media controller, and false otherwise.

The played attribute must return a new static normalized TimeRanges object that represents the union of the ranges of the media resources of the slaved media elements that the user agent has so far rendered, at the time the attribute is evaluated.

When the pause() method is invoked, if the MediaController is a playing media controller then the user agent must change the MediaController into a paused media controller, queue a task to fire a simple event named pause at the MediaController, and then report the controller state of the MediaController.

When the play() method is invoked, if the MediaController is a paused media controller, the user agent must change the MediaController into a playing media controller, queue a task to fire a simple event named play at the MediaController, and then report the controller state of the MediaController.

A MediaController has a media controller default playback rate and a media controller playback rate, which must both be set to 1.0 when the MediaController object is created.

The defaultPlaybackRate attribute, on getting, must return the MediaController's media controller default playback rate, and on setting, must set the MediaController's media controller default playback rate to the new value, then queue a task to fire a simple event named ratechange at the MediaController.

The playbackRate attribute, on getting, must return the MediaController's media controller playback rate, and on setting, must set the MediaController's media controller playback rate to the new value, then queue a task to fire a simple event named ratechange at the MediaController.

A MediaController has a media controller volume multiplier, which must be set to 1.0 when the MediaController object is created, and a media controller mute override, much must initially be false.

The volume attribute, on getting, must return the MediaController's media controller volume multiplier, and on setting, if the new value is in the range 0.0 to 1.0 inclusive, must set the MediaController's media controller volume multiplier to the new value and queue a task to fire a simple event named volumechange at the MediaController. If the new value is outside the range 0.0 to 1.0 inclusive, then, on setting, an INDEX_SIZE_ERR exception must be raised instead.

The muted attribute, on getting, must return the MediaController's media controller mute override, and on setting, must set the MediaController's media controller mute override to the new value and queue a task to fire a simple event named volumechange at the MediaController.

The media resources of all the slaved media elements of a MediaController have a defined temporal relationship which provides relative offsets between the zero time of each such media resource: for media resources with a timeline offset, their relative offsets are the difference between their timeline offset; the zero times of all the media resources without a timeline offset are not offset from each other (i.e. the origins of their timelines are cotemporal); and finally, the zero time of the media resource with the earliest timeline offset (if any) is not offset from the zero times of the media resources without a timeline offset (i.e. the origins of media resources without a timeline offset are further cotemporal with the earliest defined point on the timeline of the media resource with the earliest timeline offset).

The media resource end position of a media resource in a media element is defined as follows: if the media resource has a finite and known duration, the media resource end position is the duration of the media resource's timeline (the last defined position on that timeline); otherwise, the media resource's duration is infinite or unknown, and the media resource end position is the time of the last frame of media data currently available for that media resource.

Each MediaController also has its own defined timeline. On this timeline, all the media resources of all the slaved media elements of the MediaController are temporally aligned according to their defined offsets. The media controller duration of that MediaController is the time from the earliest earliest possible position, relative to this MediaController timeline, of any of the media resources of the slaved media elements of the MediaController, to the time of the latest media resource end position of the media resources of the slaved media elements of the MediaController, again relative to this MediaController timeline.

Each MediaController has a media controller position. This is the time on the MediaController's timeline at which the user agent is trying to play the slaved media elements. When a MediaController is created, its media controller position is initially zero.

When the user agent is to bring a media element up to speed with its new media controller, it must seek that media element to the MediaController's media controller position relative to the media element's timeline, discarding any resulting exceptions.

When the user agent is to seek the media controller to a particular new playback position, it must follow these steps:

If the new playback position is less than zero, then set it to zero.
If the new playback position is greater than the media controller duration, then set it to the media controller duration.
Set the media controller position to the new playback position.
Seek each slaved media element to the new playback position relative to the media element timeline, discarding any resulting exceptions.

A MediaController is a blocked media controller if the MediaController is a paused media controller, or if any of its slaved media elements are blocked media elements, or if any of its slaved media elements whose autoplaying flag is true still have a paused attribute that is true, or if all of its slaved media elements have their paused attribute set to true.

A media element is blocked on its media controller if the MediaController is a blocked media controller, or if its media controller position is either before the media resource's earliest possible position relative to the MediaController's timeline or after the end of the media resource relative to the MediaController's timeline.

When a MediaController is not a blocked media controller and it has at least one slaved media element whose Document is a fully active Document, the MediaController's media controller position must increase monotonically at media controller playback rate units of time on the MediaController's timeline per unit time of the clock used by its slaved media elements.

When the zero point on the timeline of a MediaController moves relative to the timelines of the slaved media elements by a time difference ΔT, the MediaController's media controller position must be decremented by ΔT.

In some situations, e.g. when playing back a live stream without buffering anything, the media controller position would increase motonically as described above at the same rate as the ΔT described in the previous paragraph decreases it, with the end result that for all intents and purposes, the media controller position would appear to remain constant (probably with the value 0).

A MediaController has a most recently reported readiness state, which is a number from 0 to 4 derived from the numbers used for the media element readyState attribute, and a most recently reported playback state, which is either playing, waiting, or ended.

When a MediaController is created, its most recently reported readiness state must be set to 0, and its most recently reported playback state must be set to waiting.

When a user agent is required to report the controller state for a MediaController, the user agent must run the following steps:

If the MediaController has no slaved media elements, let new readiness state be 0.

Otherwise, let it have the lowest value of the readyState IDL attributes of all of its slaved media elements.
If the MediaController's most recently reported readiness state is not equal to new readiness state then queue a task to fire a simple event at the MediaController object, whose name is the event name corresponding to the value of new readiness state given in the table below:

Value of new readiness state Event name
0 emptied
1 loadedmetadata
2 loadeddata
3 canplay
4 canplaythrough
Let the MediaController's most recently reported readiness state be new readiness state.
Initialize new playback state by setting it to the state given for the first matching condition from the following list:

If the MediaController has no slaved media elements

Let new playback state be waiting.

If all of the MediaController's slaved media elements have ended playback and the media controller playback rate is positive or zero

Let new playback state be ended.

If the MediaController is a blocked media controller

Let new playback state be waiting.

Otherwise

Let new playback state be playing.
If the MediaController's most recently reported playback state is not equal to new playback state then queue a task to fire a simple event at the MediaController object, whose name is playing if new playback state is playing, ended if new playback state is ended, and waiting otherwise.
Let the MediaController's most recently reported playback state be new playback state.

Value of `new readiness state`	Event name
0	`emptied`
1	`loadedmetadata`
2	`loadeddata`
3	`canplay`
4	`canplaythrough`

The following are the event handlers that must be supported, as IDL attributes, by all objects implementing the MediaController interface:

Event handler	Event handler event type
`onemptied`	`emptied`
`onloadedmetadata`	`loadedmetadata`
`onloadeddata`	`loadeddata`
`oncanplay`	`canplay`
`oncanplaythrough`	`canplaythrough`
`onplaying`	`playing`
`onwaiting`	`waiting`
`ondurationchange`	`durationchange`
`ontimeupdate`	`durationchange`
`onplay`	`play`
`onpause`	`pause`
`onratechange`	`ratechange`
`onvolumechange`	`volumechange`

The task source for the tasks listed in this section is the DOM manipulation task source.

4.8.10.11.3 Assigning a media controller declaratively

The mediagroup content attribute on media elements can be used to link multiple media elements together by implicitly creating a MediaController.

When a media element is created with a mediagroup attribute, and when a media element's mediagroup attribute is set, changed, or removed, the user agent must run the following steps:

Let m be the media element in question.
Let m have no current media controller, if it currently has one.
If m's mediagroup attribute is being removed, then abort these steps.
If there is another media element whose Document is the same as m's Document (even if one or both of these elements are not actually in the Document), and which also has a mediagroup attribute, and whose mediagroup attribute has the same value as the new value of m's mediagroup attribute, then let controller be that media element's current media controller.

Otherwise, let controller be a newly created MediaController.
Let m's current media controller be controller.
Bring the media element up to speed with its new media controller.

The mediaGroup IDL attribute on media elements must reflect the mediagroup content attribute.

Multiple media elements referencing the same media resource will share a single network request. This can be used to efficiently play two (video) tracks from the same media resource in two different places on the screen. Used with the mediagroup attribute, these elements can also be kept synchronised.

In this example, a sign-languge interpreter track from a movie file is overlaid on the primary video track of that same video file using two video elements, some CSS, and an implicit MediaController:

<article>
 <style scoped>
  div { margin: 1em auto; position: relative; width: 400px; height: 300px; }
  video { position; absolute; bottom: 0; right: 0; }
  video:first-child { width: 100%; height: 100%; }
  video:last-child { width: 30%; }
 </style>
 <div>
  <video src="movie.vid#track=Video&amp;track=English" autoplay controls mediagroup=movie></video>
  <video src="movie.vid#track=sign" autoplay mediagroup=movie></video>
 </div>
</article>

4.8.10.12 Timed text tracks

4.8.10.12.1 Text track model

A media element can have a group of associated text tracks, known as the media element's list of text tracks. The text tracks are sorted as follows:

The text tracks corresponding to track element children of the media element, in tree order.
Any text tracks added using the addTextTrack() method, in the order they were added, oldest first.
Any media-resource-specific text tracks (text tracks corresponding to data in the media resource), in the order defined by the media resource's format specification.

A text track consists of:

The kind of text track

This decides how the track is handled by the user agent. The kind is represented by a string. The possible strings are:

subtitles
captions
descriptions
chapters
metadata

The kind of track can change dynamically, in the case of a text track corresponding to a track element.

A label

This is a human-readable string intended to identify the track for the user. In certain cases, the label might be generated automatically.

The label of a track can change dynamically, in the case of a text track corresponding to a track element or in the case of an automatically-generated label whose value depends on variable factors such as the user's preferred user interface language.

A language

This is a string (a BCP 47 language tag) representing the language of the text track's cues. [BCP47]

The language of a text track can change dynamically, in the case of a text track corresponding to a track element.

A readiness state

One of the following:

Not loaded: Indicates that the text track is known to exist (e.g. it has been declared with a track element), but its cues have not been obtained.
Loading: Indicates that the text track is loading and there have been no fatal errors encountered so far. Further cues might still be added to the track.
Loaded: Indicates that the text track has been loaded with no fatal errors. No new cues will be added to the track except if the text track corresponds to a MutableTextTrack object.
Failed to load: Indicates that the text track was enabled, but when the user agent attempted to obtain it, this failed in some way (e.g. URL could not be resolved, network error, unknown text track format). Some or all of the cues are likely missing and will not be obtained.

The readiness state of a text track changes dynamically as the track is obtained.

A mode

One of the following:

Disabled

Indicates that the text track is not active. Other than for the purposes of exposing the track in the DOM, the user agent is ignoring the text track. No cues are active, no events are fired, and the user agent will not attempt to obtain the track's cues.

Hidden

Indicates that the text track is active, but that the user agent is not actively displaying the cues. If no attempt has yet been made to obtain the track's cues, the user agent will perform such an attempt momentarily. The user agent is maintaining a list of which cues are active, and events are being fired accordingly.

Showing

Showing by default

Indicates that the text track is active. If no attempt has yet been made to obtain the track's cues, the user agent will perform such an attempt momentarily. The user agent is maintaining a list of which cues are active, and events are being fired accordingly. In addition, for text tracks whose kind is subtitles or captions, the cues are being displayed over the video as appropriate; for text tracks whose kind is descriptions, the user agent is making the cues available to the user in a non-visual fashion; and for text tracks whose kind is chapters, the user agent is making available to the user a mechanism by which the user can navigate to any point in the media resource by selecting a cue.

The showing by default state is used in conjunction with the default attribute on track elements to indicate that the text track was enabled due to that attribute. This allows the user agent to override the state if a later track is discovered that is more appropriate per the user's preferences.

A list of zero or more cues

A list of text track cues, along with rules for updating the text track rendering.

The list of cues of a text track can change dynamically, either because the text track has not yet been loaded or is still loading, or because the text track corresponds to a MutableTextTrack object, whose API allows individual cues can be added or removed dynamically.

Each text track has a corresponding TextTrack object.

The text tracks of a media element are ready if all the text tracks whose mode was not in the disabled state when the element's resource selection algorithm last started now have a text track readiness state of loaded or failed to load.

A text track cue is the unit of time-sensitive data in a text track, corresponding for instance for subtitles and captions to the text that appears at a particular time and disappears at another time.

Each text track cue consists of:

An identifier: An arbitrary string.
A start time: A time, in seconds and fractions of a second, at which the cue becomes relevant.
An end time: A time, in seconds and fractions of a second, at which the cue stops being relevant.
A pause-on-exit flag: A boolean indicating whether playback of the media resource is to pause when the cue stops being relevant.
A writing direction: A writing direction, either horizontal (a line extends horizontally and is positioned vertically, with consecutive lines displayed below each other), vertical growing left (a line extends vertically and is positioned horizontally, with consecutive lines displayed to the left of each other), or vertical growing right (a line extends vertically and is positioned horizontally, with consecutive lines displayed to the right of each other).
A size: A number giving the size of the box within which the text of each line of the cue is to be aligned, to be interpreted as a percentage of the video, as defined by the writing direction.
The text of the cue: The raw text of the cue, and rules for its interpretation, allowing the text to be rendered and converted to a DOM fragment.

A text track cue is immutable.

Each text track cue has a corresponding TextTrackCue object, and can be associated with a particular text track. Once a text track cue is associated with a particular text track, the association is permanent.

In addition, each text track cue has two pieces of dynamic information:

The active flag

This flag must be initially unset. The flag is used to ensure events are fired appropriately when the cue becomes active or inactive, and to make sure the right cues are rendered.

The user agent must synchronously unset this flag whenever the text track cue is removed from its text track's text track list of cues; whenever the text track itself is removed from its media element's list of text tracks or has its text track mode changed to disabled; and whenever the media element's readyState is changed back to HAVE_NOTHING. When the flag is unset in this way for one or more cues in text tracks that were showing or showing by default prior to the relevant incident, the user agent must, after having unset the flag for all the affected cues, apply the rules for updating the text track rendering of those text tracks.

The display state

This is used as part of the rendering model, to keep cues in a consistent position. It must initially be empty. Whenever the text track cue active flag is unset, the user agent must empty the text track cue display state.

The text track cues of a media element's text tracks are ordered relative to each other in the text track cue order, which is determined as follows: first group the cues by their text track, with the groups being sorted in the same order as their text tracks appear in the media element's list of text tracks; then, within each group, cues must be sorted by their start time, earliest first; then, any cues with the same start time must be sorted by their end time, earliest first; and finally, any cues with identical end times must be sorted in the order they were created (so e.g. for cues from a WebVTT file, that would be the order in which the cues were listed in the file).

4.8.10.12.2 Sourcing in-band text tracks

A media-resource-specific text track is a text track that corresponds to data found in the media resource.

Rules for processing and rendering such data are defined by the relevant specifications, e.g. the specification of the video format if the media resource is a video.

When a media resource contains data that the user agent recognises and supports as being equivalent to a text track, the user agent runs the steps to expose a media-resource-specific text track with the relevant data, as follows:

Associate the relevant data with a new text track and its corresponding new TextTrack object. The text track is a media-resource-specific text track.
Set the new text track's kind, label, and language based on the semantics of the relevant data, as defined by the relevant specification.
Populate the new text track's list of cues with the cues parsed so far, folllowing the guidelines for exposing cues, and begin updating it dynamically as necessary.
Set the new text track's readiness state to the value that most correctly describes the current state, and begin updating it dynamically as necessary.

For example, if the relevant data in the media resource has been fully parsed and completely describes the cues, then the text track would be loaded. On the other hand, if the data for the cues is interleaved with the media data, and the media resource as a whole is still being downloaded, then the loading state might be more accurate.
Set the new text track's mode to the mode consistent with the user's preferences and the requirements of the relevant specification for the data.
Leave the text track list of cues empty, and associate with it the rules for updating the text track rendering appropriate for the format in question.
Add the new text track to the media element's list of text tracks.

When a media element is to forget the media element's media-resource-specific text tracks, the user agent must remove from the media element's list of text tracks all the media-resource-specific text tracks.

4.8.10.12.3 Sourcing out-of-band text tracks

When a track element is created, it must be associated with a new text track (with its value set as defined below) and its corresponding new TextTrack object.

The text track kind is determined from the state of the element's kind attribute according to the following table; for a state given in a cell of the first column, the kind is the string given in the second column:

State	String
Subtitles	`subtitles`
Captions	`captions`
Descriptions	`descriptions`
Chapters	`chapters`
Metadata	`metadata`

The text track label is the element's track label.

The text track language is the element's track language, if any, or the empty string otherwise.

As the kind, label, and srclang attributes are set, changed, or removed, the text track must update accordingly, as per the definitions above.

Changes to the track URL are handled in the algorithm below.

The text track list of cues is initially empty. It is dynamically modified when the referenced file is parsed. Associated with the list are the rules for updating the text track rendering appropriate for the format in question; for WebVTT, this is the rules for updating the display of WebVTT text tracks.

When a track element's parent element changes and the new parent is a media element, then the user agent must add the track element's corresponding text track to the media element's list of text tracks.

When a track element's parent element changes and the old parent was a media element, then the user agent must remove the track element's corresponding text track from the media element's list of text tracks.

When a text track corresponding to a track element is added to a media element's list of text tracks, the user agent must set the text track mode appropriately, as determined by the following conditions:

If the text track kind is subtitles or captions and the user has indicated an interest in having a track with this text track kind, text track language, and text track label enabled, and there is no other text track in the media element's list of text tracks with a text track kind of either subtitles or captions whose text track mode is showing

If the text track kind is descriptions and the user has indicated an interest in having text descriptions with this text track language and text track label enabled, and there is no other text track in the media element's list of text tracks with a text track kind of descriptions whose text track mode is showing

If the text track kind is chapters and the text track language is one that the user agent has reason to believe is appropriate for the user, and there is no other text track in the media element's list of text tracks with a text track kind of chapters whose text track mode is showing

Let the text track mode be showing.

If there is a text track in the media element's list of text tracks whose text track mode is showing by default, the user agent must furthermore change that text track's text track mode to hidden.

If the track element has a default attribute specified, and there is no other text track in the media element's list of text tracks whose text track mode is showing or showing by default

Let the text track mode be showing by default.

Otherwise

Let the text track mode be disabled.

When a text track corresponding to a track element is created with text track mode set to hidden, showing, or showing by default, and when a text track corresponding to a track element is created with text track mode set to disabled and subsequently changes its text track mode to hidden, showing, or showing by default for the first time, the user agent must immediately and synchronously run the following algorithm. This algorithm interacts closely with the event loop mechanism; in particular, it has a synchronous section (which is triggered as part of the event loop algorithm). The step in that section is marked with ⌛.

Set the text track readiness state to loading.
Let URL be the track URL of the track element.
Asynchronously run the remaining steps, while continuing with whatever task was responsible for creating the text track or changing the text track mode.
Download: If URL is not the empty string, and its origin is the same as the media element's Document's origin, then fetch URL, from the media element's Document's origin, with the force same-origin flag set.

The tasks queued by the fetching algorithm on the networking task source to process the data as it is being fetched must examine the resource's Content Type metadata, once it is available, if it ever is. If no Content Type metadata is ever available, or if the type is not recognised as a text track format, then the resource's format must be assumed to be unsupported (this causes the load to fail, as described below). If a type is obtained, and represents a supported text track format, then the resource's data must be passed to the appropriate parser as it is received, with the text track list of cues being used for that parser's output.

If the fetching algorithm fails for any reason (network error, the server returns an error code, a cross-origin check fails, etc), or if URL is the empty string or has the wrong origin as determined by the condition at the start of this step, or if the fetched resource is not in a supported format, then queue a task to first change the text track readiness state to failed to load and then fire a simple event named error at the track element; and then, once that task is queued, move on to the step below labeled monitoring.

If the fetching algorithm does not fail, then, when it completes, queue a task to first change the text track readiness state to loaded and then fire a simple event named load at the track element; and then, once that task is queued, move on to the step below labeled monitoring.

If, while the fetching algorithm is active, either:
- the track URL changes so that it is no longer equal to URL, while the text track mode is set to hidden, showing, or showing by default; or
- the text track mode changes to hidden, showing, or showing by default, while the track URL is not equal to URL
...then the user agent must run the following steps:
1. Abort the fetching algorithm.
2. Queue a task to fire a simple event named abort at the track element.
3. Let URL be the new track URL.
4. Jump back to the top of the step labeled download.
Until one of the above circumstances occurs, the user agent must remain on this step.
Monitoring: Wait until the track URL is no longer equal to URL, at the same time as the text track mode is set to hidden, showing, or showing by default.
Wait until the text track readiness state is no longer set to loading.
Await a stable state. The synchronous section consists of the following step. (The step in the synchronous section is marked with ⌛.)
⌛ Set the text track readiness state to loading.
End the synchronous section, continuing the remaining steps asynchronously.
Jump to the step labeled download.

4.8.10.12.4 Text track API

media . textTracks . length: Returns the number of text tracks associated with the media element (e.g. from track elements). This is the number of text tracks in the media element's list of text tracks.
media . textTracks[ n ]: Returns the TextTrack object representing the nth text track in the media element's list of text tracks.
track . track: Returns the TextTrack object representing the track element's text track.

The textTracks attribute of media elements must return an array host object for objects of type TextTrack that is fixed length and read only. The same object must be returned each time the attribute is accessed. [WEBIDL]

The array must contain the TextTrack objects of the text tracks in the media element's list of text tracks, in the same order as in the list of text tracks.

interface TextTrack {
  readonly attribute DOMString kind;
  readonly attribute DOMString label;
  readonly attribute DOMString language;

  const unsigned short NONE = 0;
  const unsigned short LOADING = 1;
  const unsigned short LOADED = 2;
  const unsigned short ERROR = 3;
  readonly attribute unsigned short readyState;
           attribute Function onload;
           attribute Function onerror;

  const unsigned short OFF = 0;
  const unsigned short HIDDEN = 1;
  const unsigned short SHOWING = 2;
           attribute unsigned short mode;

  readonly attribute TextTrackCueList cues;
  readonly attribute TextTrackCueList activeCues;

           attribute Function oncuechange;
};
TextTrack implements EventTarget;

textTrack . kind

Returns the text track kind string.

textTrack . label

Returns the text track label.

textTrack . language

Returns the text track language string.

textTrack . readyState

Returns the text track readiness state, represented by a number from the following list:

TextTrack . NONE (0): The text track not loaded state.
TextTrack . LOADING (1): The text track loading state.
TextTrack . LOADED (2): The text track loaded state.
TextTrack . ERROR (3): The text track failed to load state.

textTrack . mode

Returns the text track mode, represented by a number from the following list:

TextTrack . OFF (0): The text track disabled mode.
TextTrack . HIDDEN (1): The text track hidden mode.
TextTrack . SHOWING (2): The text track showing and showing by default modes.

Can be set, to change the mode.

textTrack . cues

Returns the text track list of cues, as a TextTrackCueList object.

textTrack . activeCues

Returns the text track cues from the text track list of cues that are currently active (i.e. that start before the current playback position and end after it), as a TextTrackCueList object.

The kind attribute must return the text track kind of the text track that the TextTrack object represents.

The label attribute must return the text track label of the text track that the TextTrack object represents.

The language attribute must return the text track language of the text track that the TextTrack object represents.

The readyState attribute must return the numeric value corresponding to the text track readiness state of the text track that the TextTrack object represents, as defined by the following list:

NONE (numeric value 0): The text track not loaded state.
LOADING (numeric value 1): The text track loading state.
LOADED (numeric value 2): The text track loaded state.
ERROR (numeric value 3): The text track failed to load state.

The mode attribute, on getting, must return the numeric value corresponding to the text track mode of the text track that the TextTrack object represents, as defined by the following list:

OFF (numeric value 0): The text track disabled mode.
HIDDEN (numeric value 1): The text track hidden mode.
SHOWING (numeric value 2): The text track showing and showing by default modes.

On setting, if the new value is not either 0, 1, or 2, the user agent must throw an INVALID_ACCESS_ERR exception. Otherwise, if the new value isn't equal to what the attribute would currently return, the new value must be processed as follows:

If the new value is 0

Set the text track mode of the text track that the TextTrack object represents to the text track disabled mode.

If the new value is 1

Set the text track mode of the text track that the TextTrack object represents to the text track hidden mode.

If the new value is 2

Set the text track mode of the text track that the TextTrack object represents to the text track showing mode.

If the mode had been showing by default, this will change it to showing, even though the value of mode would appear not to change.

If the text track mode of the text track that the TextTrack object represents is not the text track disabled mode, then the cues attribute must return a live TextTrackCueList object that represents the subset of the text track list of cues of the text track that the TextTrack object represents whose start times occur before the earliest possible position when the script started, in text track cue order. Otherwise, it must return null. When an object is returned, the same object must be returned each time.

The earliest possible position when the script started is whatever the earliest possible position was the last time the event loop reached step 1.

If the text track mode of the text track that the TextTrack object represents is not the text track disabled mode, then the activeCues attribute must return a live TextTrackCueList object that represents the subset of the text track list of cues of the text track that the TextTrack object represents whose active flag was set when the script started, in text track cue order. Otherwise, it must return null. When an object is returned, the same object must be returned each time.

A text track cue's active flag was set when the script started if its text track cue active flag was set the last time the event loop reached step 1.

interface MutableTextTrack : TextTrack {
 void addCue(in TextTrackCue cue);
 void removeCue(in TextTrackCue cue);
};

mutableTextTrack = media . addTextTrack( kind [, label [, language ] ] )

Creates and returns a new MutableTextTrack object, which is also added to the media element's list of text tracks.

mutableTextTrack . addCue( cue )

Adds the given cue to mutableTextTrack's text track list of cues.

Raises an exception if the argument is null, associated with another text track, or already in the list of cues.

mutableTextTrack . removeCue( cue )

Removes the given cue from mutableTextTrack's text track list of cues.

Raises an exception if the argument is null, associated with another text track, or not in the list of cues.

The addTextTrack(kind, label, language) method of media elements, when invoked, must run the following steps:

If kind is not one of the following strings, then throw a SYNTAX_ERR exception and abort these steps:
- subtitles
- captions
- descriptions
- chapters
- metadata
If the label argument was omitted, let label be the empty string.
If the language argument was omitted, let language be the empty string.
Create a new text track, and set its text track kind to kind, its text track label to label, its text track language to language, its text track readiness state to the text track loaded state, its text track mode to the text track hidden mode, and its text track list of cues to an empty list.
Add the new text track to the media element's list of text tracks.

The addCue(cue) method of MutableTextTrack objects, when invoked, must run the following steps:

If cue is null, then throw an INVALID_ACCESS_ERR exception and abort these steps.
If the given cue is already associated with a text track other than the method's MutableTextTrack object's text track, then throw an INVALID_STATE_ERR exception and abort these steps.
Associate cue with the method's MutableTextTrack object's text track, if it is not currently associated with a text track.
If the given cue is already listed in the method's MutableTextTrack object's text track's text track list of cues, then throw an INVALID_STATE_ERR exception.
Add cue to the method's MutableTextTrack object's text track's text track list of cues.

The removeCue(cue) method of MutableTextTrack objects, when invoked, must run the following steps:

If cue is null, then throw an INVALID_ACCESS_ERR exception and abort these steps.
If the given cue is not associated with the method's MutableTextTrack object's text track, then throw an INVALID_STATE_ERR exception.
If the given cue is not currently listed in the method's MutableTextTrack object's text track's text track list of cues, then throw a NOT_FOUND_ERR exception.
Remove cue from the method's MutableTextTrack object's text track's text track list of cues.

In this example, an audio element is used to play a specific sound-effect from a sound file containing many sound effects. A cue is used to pause the audio, so that it ends exactly at the end of the clip, even if the browser is busy running some script. If the page had relied on script to pause the audio, then the start of the next clip might be heard if the browser was not able to run the script at the exact time specified.

var sfx = new Audio('sfx.wav');
var sounds = a.addTextTrack('metadata');

// add sounds we care about
sounds.addCue(new TextTrackCue('dog bark', 12.783, 13.612, '', '', '', true));
sounds.addCue(new TextTrackCue('kitten mew', 13.612, 15.091, '', '', '', true));

function playSound(id) {
  sfx.currentTime = sounds.getCueById(id).startTime;
  sfx.play();
}

sfx.oncanplaythrough = function () {
  playSound('dog bark');
}
window.onbeforeunload = function () {
  playSound('kitten mew');
  return 'Are you sure you want to leave this awesome page?';
}

interface TextTrackCueList {
  readonly attribute unsigned long length;
  getter TextTrackCue (in unsigned long index);
  TextTrackCue getCueById(in DOMString id);
};

cuelist . length

Returns the number of cues in the list.

cuelist[index]

Returns the text track cue with index index in the list. The cues are sorted in text track cue order.

cuelist . getCueById( id )

Returns the first text track cue (in text track cue order) with text track cue identifier id.

Returns null if none of the cues have the given identifier or if the argument is the empty string.

A TextTrackCueList object represents a dynamically updating list of text track cues in a given order.

The length attribute must return the number of cues in the list represented by the TextTrackCueList object.

The supported property indicies of a TextTrackCueList object at any instant are the numbers from zero to the number of cues in the list represented by the TextTrackCueList object minus one, if any. If there are no cues in the list, there are no supported property indicies.

To determine the value of an indexed property for a given index index, the user agent must return the indexth text track cue in the list represented by the TextTrackCueList object.

The getCueById(id) method, when called with an argument other than the empty string, must return the first text track cue in the list represented by the TextTrackCueList object whose text track cue identifier is id, if any, or null otherwise. If the argument is the empty string, then the method must return null.

interface TextTrackCue {
  readonly attribute TextTrack track;
  readonly attribute DOMString id;

  readonly attribute double startTime;
  readonly attribute double endTime;
  readonly attribute boolean pauseOnExit;


  DOMString getCueAsSource();
  DocumentFragment getCueAsHTML();

           attribute Function onenter;
           attribute Function onexit;
};
TextTrackCue implements EventTarget;

cue . track: Returns the TextTrack object to which this text track cue belongs, if any, or null otherwise.
cue . id: Returns the text track cue identifier.
cue . startTime: Returns the text track cue start time, in seconds.
cue . endTime: Returns the text track cue end time, in seconds.
cue . pauseOnExit: Returns true if the text track cue pause-on-exit flag is set, false otherwise.
source = cue . getCueAsSource(): Returns the text track cue text in raw unparsed form.
fragment = cue . getCueAsHTML(): Returns the text track cue text as a DocumentFragment of HTML elements and other DOM nodes.

The track attribute must return the TextTrack object of the text track with which the text track cue that the TextTrackCue object represents is associated, if any; or null otherwise.

The id attribute must return the text track cue identifier of the text track cue that the TextTrackCue object represents.

The startTime attribute must return the text track cue start time of the text track cue that the TextTrackCue object represents, in seconds.

The endTime attribute must return the text track cue end time of the text track cue that the TextTrackCue object represents, in seconds.

The pauseOnExit attribute must return true if the text track cue pause-on-exit flag of the text track cue that the TextTrackCue object represents is set; or false otherwise.

The direction attribute must return the text track cue writing direction of the text track cue that the TextTrackCue object represents.

The getCueAsSource() method must return the raw text track cue text.

The getCueAsHTML() method must convert the text track cue text to a DocumentFragment for the media element's Document, using the appropriate rules for doing so.

4.8.10.12.5 Event definitions

The following are the event handlers that must be supported, as IDL attributes, by all objects implementing the TextTrack interface:

Event handler	Event handler event type
`onload`	`load`
`onerror`	`error`
`oncuechange`	`cuechange`

The following are the event handlers that must be supported, as IDL attributes, by all objects implementing the TextTrackCue interface:

Event handler	Event handler event type
`onenter`	`enter`
`onexit`	`exit`

4.8.10.13 User interface

The controls attribute is a boolean attribute. If present, it indicates that the author has not provided a scripted controller and would like the user agent to provide its own set of controls.

If the attribute is present, or if scripting is disabled for the media element, then the user agent should expose a user interface to the user. This user interface should include features to begin playback, pause playback, seek to an arbitrary position in the content (if the content supports arbitrary seeking), change the volume, change the display of closed captions or embedded sign-language tracks, select different audio tracks or turn on audio descriptions, and show the media content in manners more suitable to the user (e.g. full-screen video or in an independent resizable window). Other controls may also be made available.

If the media element has a current media controller, then the user agent should expose audio tracks from all the slaved media elements (although avoiding duplicates if the same media resource is being used several times). If a media resource's audio track exposed in this way has no known name, and it is the only audio track for a particular media element, the user agent should use the element's title attribute, if any, as the name (or as part of the name) of that track.

Even when the attribute is absent, however, user agents may provide controls to affect playback of the media resource (e.g. play, pause, seeking, and volume controls), but such features should not interfere with the page's normal rendering. For example, such features could be exposed in the media element's context menu.

Where possible (specifically, for starting, stopping, pausing, and unpausing playback, for seeking, for changing the rate of playback, for fast-forwarding or rewinding, for listing, enabling, and disabling text tracks, and for muting or changing the volume of the audio), user interface features exposed by the user agent must be implemented in terms of the DOM API described above, so that, e.g., all the same events fire.

When a media element has a current media controller, the user agent's user interface for pausing and unpausing playback, for seeking, for changing the rate of playback, for fast-forwarding or rewinding, and for muting or changing the volume of audio of the entire group must be implemented in terms of the MediaController API exposed on that current media controller.

The "play" function in the user agent's interface must set the playbackRate attribute to the value of the defaultPlaybackRate attribute before invoking the play() method. When a media element has a current media controller, the attributes and method with those names on that MediaController object must be used. Otherwise, the attributes and method with those names on the media element itself must be used.

Features such as fast-forward or rewind must be implemented by only changing the playbackRate attribute (and not the defaultPlaybackRate attribute). Again, when a media element has a current media controller, the attributes with those names on that MediaController object must be used; otherwise, the attributes with those names on the media element itself must be used.

When a media element has a current media controller, and all the slaved media elements of that MediaController are paused, the user agent should unpause all the slaved media elements when the user invokes a user agent interface control for beginning playback.

When a media element has a current media controller, seeking must be implemented in terms of the seek() method on that MediaController object. Otherwise, the user agent must directly seek to the requested position in the media element's media timeline.

When a media element has a current media controller, user agents may additionally provide the user with controls that directly manipulate an individual media element without affecting the MediaController, but such features are considered relatively advanced and unlikely to be useful to most users.

For the purposes of listing chapters in the media resource, only text tracks in the media element's list of text tracks showing or showing by default and whose text track kind is chapters should be used. Each cue in such a text track represents a chapter starting at the cue's start time. The name of the chapter is the text track cue text, interpreted literally.

The controls IDL attribute must reflect the content attribute of the same name.

media . volume [ = value ]

Returns the current playback volume, as a number in the range 0.0 to 1.0, where 0.0 is the quietest and 1.0 the loudest.

Can be set, to change the volume.

Throws an INDEX_SIZE_ERR if the new value is not in the range 0.0 .. 1.0.

media . muted [ = value ]

Returns true if audio is muted, overriding the volume attribute, and false if the volume attribute is being honored.

Can be set, to change whether the audio is muted or not.

The volume attribute must return the playback volume of any audio portions of the media element, in the range 0.0 (silent) to 1.0 (loudest). Initially, the volume must be 1.0, but user agents may remember the last set value across sessions, on a per-site basis or otherwise, so the volume may start at other values. On setting, if the new value is in the range 0.0 to 1.0 inclusive, the attribute must be set to the new value. If the new value is outside the range 0.0 to 1.0 inclusive, then, on setting, an INDEX_SIZE_ERR exception must be raised instead.

The muted attribute must return true if the audio channels are muted and false otherwise. Initially, the audio channels should not be muted (false), but user agents may remember the last set value across sessions, on a per-site basis or otherwise, so the muted state may start as muted (true). On setting, the attribute must be set to the new value.

Whenever either the muted or volume attributes are changed, the user agent must queue a task to fire a simple event named volumechange at the media element.

An element's effective media volume is determined as follows:

If the element's muted attribute is true, the element's effective media volume is zero. Abort these steps.
If the element has a current media controller and that MediaController object's media controller mute override is true, the element's effective media volume is zero. Abort these steps.
Let volume be the value of the element's volume attribute.
If the element has a current media controller, multiply volume by that MediaController object's media controller volume multiplier.
The element's effective media volume is volume, interpreted relative to the range 0.0 to 1.0, with 0.0 being silent, and 1.0 being the loudest setting, values in between increasing in loudness. The range need not be linear. The loudest setting may be lower than the system's loudest possible setting; for example the user could have set a maximum volume.

The muted attribute on the video element controls the default state of the audio channel of the media resource, potentially overriding user preferences.

When a media element is created, if it has a muted attribute specified, the user agent must set the muted IDL attribute to true, overriding any user preference.

The defaultMuted IDL attribute must reflect the muted content attribute.

This attribute has no dynamic effect (it only controls the default state of the element).

This video (an advertisment) autoplays, but to avoid annoying users, it does so without sound, and allows the user to turn the sound on.

<video src="adverts.cgi?kind=video" controls autoplay loop muted></video>

4.8.10.14 Time ranges

Objects implementing the TimeRanges interface represent a list of ranges (periods) of time.

interface TimeRanges {
  readonly attribute unsigned long length;
  double start(in unsigned long index);
  double end(in unsigned long index);
};

media . length

Returns the number of ranges in the object.

time = media . start(index)

Returns the time for the start of the range with the given index.

Throws an INDEX_SIZE_ERR if the index is out of range.

time = media . end(index)

Returns the time for the end of the range with the given index.

Throws an INDEX_SIZE_ERR if the index is out of range.

The length IDL attribute must return the number of ranges represented by the object.

The start(index) method must return the position of the start of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

The end(index) method must return the position of the end of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

These methods must raise INDEX_SIZE_ERR exceptions if called with an index argument greater than or equal to the number of ranges represented by the object.

When a TimeRanges object is said to be a normalized TimeRanges object, the ranges it represents must obey the following criteria:

The start of a range must be greater than the end of all earlier ranges.
The start of a range must be less than the end of that same range.

In other words, the ranges in such an object are ordered, don't overlap, aren't empty, and don't touch (adjacent ranges are folded into one bigger range).

The timelines used by the objects returned by the buffered, seekable and played IDL attributes of media elements must be that element's media timeline.

4.8.10.15 Event summary

This section is non-normative.

The following events fire on media elements as part of the processing model described above:

Event name	Interface	Dispatched when...	Preconditions
`loadstart`	`Event`	The user agent begins looking for media data, as part of the resource selection algorithm.	`networkState` equals `NETWORK_LOADING`
`progress`	`Event`	The user agent is fetching media data.	`networkState` equals `NETWORK_LOADING`
`suspend`	`Event`	The user agent is intentionally not currently fetching media data, but does not have the entire media resource downloaded.	`networkState` equals `NETWORK_IDLE`
`abort`	`Event`	The user agent stops fetching the media data before it is completely downloaded, but not due to an error.	`error` is an object with the code `MEDIA_ERR_ABORTED`. `networkState` equals either `NETWORK_EMPTY` or `NETWORK_IDLE`, depending on when the download was aborted.
`error`	`Event`	An error occurs while fetching the media data.	`error` is an object with the code `MEDIA_ERR_NETWORK` or higher. `networkState` equals either `NETWORK_EMPTY` or `NETWORK_IDLE`, depending on when the download was aborted.
`emptied`	`Event`	A media element whose `networkState` was previously not in the `NETWORK_EMPTY` state has just switched to that state (either because of a fatal error during load that's about to be reported, or because the `load()` method was invoked while the resource selection algorithm was already running).	`networkState` is `NETWORK_EMPTY`; all the IDL attributes are in their initial states.
`stalled`	`Event`	The user agent is trying to fetch media data, but data is unexpectedly not forthcoming.	`networkState` is `NETWORK_LOADING`.
`loadedmetadata`	`Event`	The user agent has just determined the duration and dimensions of the media resource and the text tracks are ready.	`readyState` is newly equal to `HAVE_METADATA` or greater for the first time.
`loadeddata`	`Event`	The user agent can render the media data at the current playback position for the first time.	`readyState` newly increased to `HAVE_CURRENT_DATA` or greater for the first time.
`canplay`	`Event`	The user agent can resume playback of the media data, but estimates that if playback were to be started now, the media resource could not be rendered at the current playback rate up to its end without having to stop for further buffering of content.	`readyState` newly increased to `HAVE_FUTURE_DATA` or greater.
`canplaythrough`	`Event`	The user agent estimates that if playback were to be started now, the media resource could be rendered at the current playback rate all the way to its end without having to stop for further buffering.	`readyState` is newly equal to `HAVE_ENOUGH_DATA`.
`playing`	`Event`	Playback is ready to start after having been paused or delayed due to lack of media data.	`readyState` is newly equal to or greater than `HAVE_FUTURE_DATA` and `paused` is false, or `paused` is newly false and `readyState` is equal to or greater than `HAVE_FUTURE_DATA`. Even if this event fires, the element might still not be potentially playing, e.g. if the element is blocked on its media controller (e.g. because the current media controller is paused, or another slaved media element is stalled somehow, or because the media resource has no data corresponding to the media controller position), or the element is paused for user interaction.
`waiting`	`Event`	Playback has stopped because the next frame is not available, but the user agent expects that frame to become available in due course.	`readyState` is equal to or less than `HAVE_CURRENT_DATA`, and `paused` is false. Either `seeking` is true, or the current playback position is not contained in any of the ranges in `buffered`. It is possible for playback to stop for other reasons without `paused` being false, but those reasons do not fire this event (and when those situations resolve, a separate `playing` event is not fired either): e.g. the element is newly blocked on its media controller, or playback ended, or playback stopped due to errors, or the element has paused for user interaction.
`seeking`	`Event`	The `seeking` IDL attribute changed to true and the seek operation is taking long enough that the user agent has time to fire the event.
`seeked`	`Event`	The `seeking` IDL attribute changed to false.
`ended`	`Event`	Playback has stopped because the end of the media resource was reached.	`currentTime` equals the end of the media resource; `ended` is true.
`durationchange`	`Event`	The `duration` attribute has just been updated.
`timeupdate`	`Event`	The current playback position changed as part of normal playback or in an especially interesting way, for example discontinuously.
`play`	`Event`	The element is no longer paused. Fired after the `play()` method has returned, or when the `autoplay` attribute has caused playback to begin.	`paused` is newly false.
`pause`	`Event`	The element has been paused. Fired after the `pause()` method has returned.	`paused` is newly true.
`ratechange`	`Event`	Either the `defaultPlaybackRate` or the `playbackRate` attribute has just been updated.
`volumechange`	`Event`	Either the `volume` attribute or the `muted` attribute has changed. Fired after the relevant attribute's setter has returned.

The following events fire on MediaController objects:

Event name	Interface	Dispatched when...
`emptied`	`Event`	All the slaved media elements newly have `readyState` set to `HAVE_NOTHING` or greater, or there are no longer any slaved media elements.
`loadedmetadata`	`Event`	All the slaved media elements newly have `readyState` set to `HAVE_METADATA` or greater.
`loadeddata`	`Event`	All the slaved media elements newly have `readyState` set to `HAVE_CURRENT_DATA` or greater.
`canplay`	`Event`	All the slaved media elements newly have `readyState` set to `HAVE_FUTURE_DATA` or greater.
`canplaythrough`	`Event`	All the slaved media elements newly have `readyState` set to `HAVE_ENOUGH_DATA` or greater.
`playing`	`Event`	The `MediaController` is no longer a blocked media controller.
`waiting`	`Event`	The `MediaController` is now a blocked media controller.
`ended`	`Event`	All the slaved media elements have newly ended playback.
`durationchange`	`Event`	The `duration` attribute has just been updated.
`timeupdate`	`Event`	The media controller position changed.
`play`	`Event`	The `paused` attribute is newly false.
`pause`	`Event`	The `paused` attribute is newly true.
`ratechange`	`Event`	Either the `defaultPlaybackRate` attribute or the `playbackRate` attribute has just been updated.
`volumechange`	`Event`	Either the `volume` attribute or the `muted` attribute has just been updated.

4.8.10.16 Security and privacy considerations

The main security and privacy implications of the video and audio elements come from the ability to embed media cross-origin. There are two directions that threats can flow: from hostile content to a victim page, and from a hostile page to victim content.

If a victim page embeds hostile content, the threat is that the content might contain scripted code that attempts to interact with the Document that embeds the content. To avoid this, user agents must ensure that there is no access from the content to the embedding page. In the case of media content that uses DOM concepts, the embedded content must be treated as if it was in its own unrelated top-level browsing context.

For instance, if an SVG animation was embedded in a video element, the user agent would not give it access to the DOM of the outer page. From the perspective of scripts in the SVG resource, the SVG file would appear to be in a lone top-level browsing context with no parent.

If a hostile page embeds victim content, the threat is that the embedding page could obtain information from the content that it would not otherwise have access to. The API does expose some information: the existence of the media, its type, its duration, its size, and the performance characteristics of its host. Such information is already potentially problematic, but in practice the same information can more or less be obtained using the img element, and so it has been deemed acceptable.

However, significantly more sensitive information could be obtained if the user agent further exposes metadata within the content such as subtitles or chapter titles. This version of the API does not expose such information. Future extensions to this API will likely reuse a mechanism such as CORS to check that the embedded content's site has opted in to exposing such information. [CORS]

An attacker could trick a user running within a corporate network into visiting a site that attempts to load a video from a previously leaked location on the corporation's intranet. If such a video included confidential plans for a new product, then being able to read the subtitles would present a confidentiality breach.

4.8.10.17 Best practices for authors using media elements

This section is non-normative.

Playing audio and video resources on small devices such as set-top boxes or mobile phones is often constrained by limited hardware resources in the device. For example, a device might only support three simultaneous videos. For this reason, it is a good practice to release resources held by media elements when they are done playing, either by being very careful about removing all references to the element and allowing it to be garbage collected, or, even better, by removing the element's src attribute and any source element descendants, and invoking the element's load() method.

Similarly, when the playback rate is not exactly 1.0, hardware, software, or format limitations can cause video frames to be dropped and audio to be choppy or muted.

4.8.10.18 Best practices for implementors of media elements

This section is non-normative.

How accurately various aspects of the media element API are implemented is considered a quality-of-implementation issue.

For example, when implementing the buffered attribute, how precise an implementation reports the ranges that have been buffered depends on how carefully the user agent inspects the data. Since the API reports ranges as times, but the data is obtained in byte streams, a user agent receiving a variable-bit-rate stream might only be able to determine precise times by actually decoding all of the data. User agents aren't required to do this, however; they can instead return estimates (e.g. based on the average bit rate seen so far) which get revised as more information becomes available.

As a general rule, user agents are urged to be conservative rather than optimistic. For example, it would be bad to report that everything had been buffered when it had not.

Another quality-of-implementation issue would be playing a video backwards when the codec is designed only for forward playback (e.g. there aren't many key frames, and they are far apart, and the intervening frames only have deltas from the previous frame). User agents could do a poor job, e.g. only showing key frames; however, better implementations would do more work and thus do a better job, e.g. actually decoding parts of the video forwards, storing the complete frames, and then playing the frames backwards.

Similarly, while implementations are allowed to drop buffered data at any time (there is no requirement that a user agent keep all the media data obtained for the lifetime of the media element), it is again a quality of implementation issue: user agents with sufficient resources to keep all the data around are encouraged to do so, as this allows for a better user experience. For example, if the user is watching a live stream, a user agent could allow the user only to view the live video; however, a better user agent would buffer everything and allow the user to seek through the earlier material, pause it, play it forwards and backwards, etc.

When multiple tracks are synchronised with a MediaController, it is possible for scripts to add and remove media elements from the MediaController's list of slaved media elements, even while these tracks are playing. How smoothly the media plays back in such situations is another quality-of-implementation issue.

When a media element that is paused is removed from a document and not reinserted before the next time the event loop spins, implementations that are resource constrained are encouraged to take that opportunity to release all hardware resources (like video planes, networking resources, and data buffers) used by the media element. (User agents still have to keep track of the playback position and so forth, though, in case playback is later restarted.)

4.8.11 The `canvas` element

Categories

Contexts in which this element can be used:

Where embedded content is expected.

Content model:

Transparent.

Content attributes:

width

height

DOM interface:

interface HTMLCanvasElement : HTMLElement {
           attribute unsigned long width;
           attribute unsigned long height;

  DOMString toDataURL(in optional DOMString type, in any... args);
  void toBlob(in FileCallback, in optional DOMString type, in any... args);

  object getContext(in DOMString contextId, in any... args);
};

The canvas element provides scripts with a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, or other visual images on the fly.

Authors should not use the canvas element in a document when a more suitable element is available. For example, it is inappropriate to use a canvas element to render a page heading: if the desired presentation of the heading is graphically intense, it should be marked up using appropriate elements (typically h1) and then styled using CSS and supporting technologies such as XBL.

When authors use the canvas element, they must also provide content that, when presented to the user, conveys essentially the same function or purpose as the bitmap canvas. This content may be placed as content of the canvas element. The contents of the canvas element, if any, are the element's fallback content.

In interactive visual media, if scripting is enabled for the canvas element, and if support for canvas elements has been enabled, the canvas element represents embedded content consisting of a dynamically created image.

In non-interactive, static, visual media, if the canvas element has been previously painted on (e.g. if the page was viewed in an interactive visual medium and is now being printed, or if some script that ran during the page layout process painted on the element), then the canvas element represents embedded content with the current image and size. Otherwise, the element represents its fallback content instead.

In non-visual media, and in visual media if scripting is disabled for the canvas element or if support for canvas elements has been disabled, the canvas element represents its fallback content instead.

When a canvas element represents embedded content, the user can still focus descendants of the canvas element (in the fallback content). When an element is focused, it is the target of keyboard interaction events (even though the element itself is not visible). This allows authors to make an interactive canvas keyboard-accessible: authors should have a one-to-one mapping of interactive regions to focusable elements in the fallback content. (Focus has no effect on mouse interaction events.) [DOMEVENTS]

The canvas element has two attributes to control the size of the coordinate space: width and height. These attributes, when specified, must have values that are valid non-negative integers. The rules for parsing non-negative integers must be used to obtain their numeric values. If an attribute is missing, or if parsing its value returns an error, then the default value must be used instead. The width attribute defaults to 300, and the height attribute defaults to 150.

The intrinsic dimensions of the canvas element equal the size of the coordinate space, with the numbers interpreted in CSS pixels. However, the element can be sized arbitrarily by a style sheet. During rendering, the image is scaled to fit this layout size.

The size of the coordinate space does not necessarily represent the size of the actual bitmap that the user agent will use internally or during rendering. On high-definition displays, for instance, the user agent may internally use a bitmap with two device pixels per unit in the coordinate space, so that the rendering remains at high quality throughout.

When the canvas element is created, and subsequently whenever the width and height attributes are set (whether to a new value or to the previous value), the bitmap and any associated contexts must be cleared back to their initial state and reinitialized with the newly specified coordinate space dimensions.

When the canvas is initialized, its bitmap must be cleared to transparent black.

The width and height IDL attributes must reflect the respective content attributes of the same name, with the same defaults.

Only one square appears to be drawn in the following example:

  // canvas is a reference to a <canvas> element
  var context = canvas.getContext('2d');
  context.fillRect(0,0,50,50);
  canvas.setAttribute('width', '300'); // clears the canvas
  context.fillRect(0,100,50,50);
  canvas.width = canvas.width; // clears the canvas
  context.fillRect(100,0,50,50); // only this square remains

context = canvas . getContext(contextId [, ... ])

Returns an object that exposes an API for drawing on the canvas. The first argument specifies the desired API. Subsequent arguments are handled by that API.

The list of defined contexts is given on the WHATWG Wiki CanvasContexts page. [WHATWGWIKI]

Returns null if the given context ID is not supported or if the canvas has already been initialised with some other (incompatible) context type (e.g. trying to get a "2d" context after getting a "webgl" context).

A canvas element can have a primary context, which is the first context to have been obtained for that element. When created, a canvas element must not have a primary context.

The most commonly used primary context is the HTML Canvas 2D Context.

The getContext(contextId, args...) method of the canvas element, when invoked, must run the following steps:

Let contextId be the first argument to the method.
If contextId is not the name of a context supported by the user agent, return null and abort these steps.

An example of this would be a user agent that theoretically supports the "webgl" 3D context, in the case where the platform does not have hardware support for OpenGL and the user agent does not have a software OpenGL implementation. Despite the user agent recognising the "webgl" name, it would return null at this step because that context is not, in practice, supported at the time of the call.
If the element has a primary context and that context's entry in the WHATWG Wiki CanvasContexts page does not list contextId as a context with which it is compatible, return null and abort these steps. [WHATWGWIKI]
If the element does not have a primary context, let the element's primary context be contextId.
If the getContext() method has already been invoked on this element for the same contextId, return the same object as was returned that time, and abort these steps. The additional arguments are ignored.
Return a new object for contextId, as defined by the specification given for contextId's entry in the WHATWG Wiki CanvasContexts page. [WHATWGWIKI]

New context types may be registered in the WHATWG Wiki CanvasContexts page. [WHATWGWIKI]

Anyone is free to edit the WHATWG Wiki CanvasContexts page at any time to add a new context type. These new context types must be specified with the following information:

Keyword: The value of contextID that will return the object for the new API.
Specification: A link to a formal specification of the context type's API. It could be another page on the Wiki, or a link to an external page. If the type does not have a formal specification, an informal description can be substituted until such time as a formal specification is available.
Compatible with: The list of context types that are compatible with this one (i.e. that operate on the same underlying bitmap). This list must be transitive and symmetric; if one context type is defined as compatible with another, then all types it is compatible with must be compatible with all types the other is compatible with.

Vendors may also define experimental contexts using the syntax vendorname-context, for example, moz-3d. Such contexts should be registered in the WHATWG Wiki CanvasContexts page.

url = canvas . toDataURL( [ type, ... ])

Returns a data: URL for the image in the canvas.

The first argument, if provided, controls the type of the image to be returned (e.g. PNG or JPEG). The default is image/png; that type is also used if the given type isn't supported. The other arguments are specific to the type, and control the way that the image is generated, as given in the table below.

When trying to use types other than "image/png", authors can check if the image was really returned in the requested format by checking to see if the returned string starts with one of the exact strings "data:image/png," or "data:image/png;". If it does, the image is PNG, and thus the requested type was not supported. (The one exception to this is if the canvas has either no height or no width, in which case the result might simply be "data:,".)

canvas . toBlob(callback [, type, ... ])

Creates a Blob object representing a file containing the image in the canvas, and invokes a callback with a handle to that object.

The second argument, if provided, controls the type of the image to be returned (e.g. PNG or JPEG). The default is image/png; that type is also used if the given type isn't supported. The other arguments are specific to the type, and control the way that the image is generated, as given in the table below.

The toDataURL() method must run the following steps:

If the canvas has no pixels (i.e. either its horizontal dimension or its vertical dimension is zero) then return the string "data:," and abort these steps. (This is the shortest data: URL; it represents the empty string in a text/plain resource.)
Let file be a serialization of the image as a file, using the method's arguments (if any) as the arguments.
Return a data: URL representing file. [RFC2397]

The toBlob() method must run the following steps:

Let callback be the first argument.
Let arguments be the second and subsequent arguments to the method, if any.
Let file be a serialization of the image as a file, using arguments.
Return, but continue running these steps asynchronously.
If callback is null, abort these steps.
Queue a task to invoke the FileCallback callback with a Blob object representing file as its argument. The task source for this task is the canvas blob serialization task source. [FILESYSTEMAPI] [FILEAPI]

When a user agent is to create a serialization of the image as a file, optionally with some given arguments, it must create an image file in the format given by the first value of arguments, or, if there are no arguments, in the PNG format. [PNG]

If arguments is not empty, the first value must be interpreted as a MIME type giving the format to use. If the type has any parameters, it must be treated as not supported.

For example, the value "image/png" would mean to generate a PNG image, the value "image/jpeg" would mean to generate a JPEG image, and the value "image/svg+xml" would mean to generate an SVG image (which would probably require that the implementation actually keep enough information to reliably render an SVG image from the canvas).

User agents must support PNG ("image/png"). User agents may support other types. If the user agent does not support the requested type, it must create the file using the PNG format. [PNG]

User agents must convert the provided type to ASCII lowercase before establishing if they support that type.

For image types that do not support an alpha channel, the serialized image must be the canvas image composited onto a solid black background using the source-over operator.

If the first argument in arguments gives a type corresponding to one of the types given in the first column of the following table, and the user agent supports that type, then the subsequent arguments, if any, must be treated as described in the second cell of that row.

Type	Other arguments	Reference
`image/jpeg`	The second argument, if it is a number in the range 0.0 to 1.0 inclusive, must be treated as the desired quality level. If it is not a number or is outside that range, the user agent must use its default value, as if the argument had been omitted.	[JPEG]

For the purposes of these rules, an argument is considered to be a number if it is converted to an IDL double value by the rules for handling arguments of type any in the Web IDL specification. [WEBIDL]

Other arguments must be ignored and must not cause the user agent to raise an exception. A future version of this specification will probably define other parameters to be passed to these methods to allow authors to more carefully control compression settings, image metadata, etc.

4.8.11.1 Color spaces and color correction

The canvas APIs must perform color correction at only two points: when rendering images with their own gamma correction and color space information onto the canvas, to convert the image to the color space used by the canvas (e.g. using the 2D Context's drawImage() method with an HTMLImageElement object), and when rendering the actual canvas bitmap to the output device.

Thus, in the 2D context, colors used to draw shapes onto the canvas will exactly match colors obtained through the getImageData() method.

The toDataURL() method must not include color space information in the resource returned. Where the output format allows it, the color of pixels in resources created by toDataURL() must match those returned by the getImageData() method.

In user agents that support CSS, the color space used by a canvas element must match the color space used for processing any colors for that element in CSS.

The gamma correction and color space information of images must be handled in such a way that an image rendered directly using an img element would use the same colors as one painted on a canvas element that is then itself rendered. Furthermore, the rendering of images that have no color correction information (such as those returned by the toDataURL() method) must be rendered with no color correction.

Thus, in the 2D context, calling the drawImage() method to render the output of the toDataURL() method to the canvas, given the appropriate dimensions, has no visible effect.

4.8.11.2 Security with `canvas` elements

Information leakage can occur if scripts from one origin can access information (e.g. read pixels) from images from another origin (one that isn't the same).

To mitigate this, canvas elements are defined to have a flag indicating whether they are origin-clean. All canvas elements must start with their origin-clean set to true. The flag must be set to false if any of the following actions occur:

The element's 2D context's drawImage() method is called with an HTMLImageElement or an HTMLVideoElement whose origin is not the same as that of the Document object that owns the canvas element.
The element's 2D context's drawImage() method is called with an HTMLCanvasElement whose origin-clean flag is false.
The element's 2D context's fillStyle attribute is set to a CanvasPattern object that was created from an HTMLImageElement or an HTMLVideoElement whose origin was not the same as that of the Document object that owns the canvas element when the pattern was created.
The element's 2D context's fillStyle attribute is set to a CanvasPattern object that was created from an HTMLCanvasElement whose origin-clean flag was false when the pattern was created.
The element's 2D context's strokeStyle attribute is set to a CanvasPattern object that was created from an HTMLImageElement or an HTMLVideoElement whose origin was not the same as that of the Document object that owns the canvas element when the pattern was created.
The element's 2D context's strokeStyle attribute is set to a CanvasPattern object that was created from an HTMLCanvasElement whose origin-clean flag was false when the pattern was created.
The element's 2D context's fillText() or strokeText() methods are invoked and consider using a font that has an origin that is not the same as that of the Document object that owns the canvas element. (The font doesn't even have to be used; all that matters is whether the font was considered for any of the glyphs drawn.)

Whenever the toDataURL() method of a canvas element whose origin-clean flag is set to false is called, the method must raise a SECURITY_ERR exception.

Whenever the getImageData() method of the 2D context of a canvas element whose origin-clean flag is set to false is called with otherwise correct arguments, the method must raise a SECURITY_ERR exception.

Whenever the measureText() method of the 2D context of a canvas element ends up using a font that has an origin that is not the same as that of the Document object that owns the canvas element, the method must raise a SECURITY_ERR exception.

Even resetting the canvas state by changing its width or height attributes doesn't reset the origin-clean flag.

4.8.12 The `map` element

Categories

When the element only contains phrasing content: phrasing content.

Contexts in which this element can be used:

When the element only contains phrasing content: where phrasing content is expected.

Otherwise: where flow content is expected.

Content model:

Transparent.

Content attributes:

name

DOM interface:

interface HTMLMapElement : HTMLElement {
           attribute DOMString name;
  readonly attribute HTMLCollection areas;
  readonly attribute HTMLCollection images;
};

The map element, in conjunction with any area element descendants, defines an image map. The element represents its children.

The name attribute gives the map a name so that it can be referenced. The attribute must be present and must have a non-empty value with no space characters. The value of the name attribute must not be a compatibility-caseless match for the value of the name attribute of another map element in the same document. If the id attribute is also specified, both attributes must have the same value.

map . areas: Returns an HTMLCollection of the area elements in the map.
map . images: Returns an HTMLCollection of the img and object elements that use the map.

The areas attribute must return an HTMLCollection rooted at the map element, whose filter matches only area elements.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img and object elements that are associated with this map element according to the image map processing model.

The IDL attribute name must reflect the content attribute of the same name.

Image maps can be defined in conjunction with other content on the page, to ease maintenance. This example is of a page with an image map at the top of the page and a corresponding set of text links at the bottom.

<!DOCTYPE HTML>
<TITLE>Babies™: Toys</TITLE>
<HEADER>
 <H1>Toys</H1>
 <IMG SRC="/images/menu.gif"
      ALT="Babies™ navigation menu. Select a department to go to its page."
      USEMAP="#NAV">
</HEADER>
 ...
<FOOTER>
 <MAP NAME="NAV">
  <P>
   <A HREF="/clothes/">Clothes</A>
   <AREA ALT="Clothes" COORDS="0,0,100,50" HREF="/clothes/"> |
   <A HREF="/toys/">Toys</A>
   <AREA ALT="Toys" COORDS="0,0,100,50" HREF="/toys/"> |
   <A HREF="/food/">Food</A>
   <AREA ALT="Food" COORDS="0,0,100,50" HREF="/food/"> |
   <A HREF="/books/">Books</A>
   <AREA ALT="Books" COORDS="0,0,100,50" HREF="/books/">
 </MAP>
</FOOTER>

4.8.13 The `area` element

Categories

Contexts in which this element can be used:

Where phrasing content is expected, but only if there is a map element ancestor.

Content model:

Empty.

Content attributes:

alt

coords

shape

href

target

rel

media

hreflang

type

DOM interface:

interface HTMLAreaElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString coords;
           attribute DOMString shape;
  stringifier attribute DOMString href;
           attribute DOMString target;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;

  // URL decomposition IDL attributes
           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
};

The area element represents either a hyperlink with some text and a corresponding area on an image map, or a dead area on an image map.

If the area element has an href attribute, then the area element represents a hyperlink. In this case, the alt attribute must be present. It specifies the text of the hyperlink. Its value must be text that, when presented with the texts specified for the other hyperlinks of the image map, and with the alternative text of the image, but without the image itself, provides the user with the same kind of choice as the hyperlink would when used without its text but with its shape applied to the image. The alt attribute may be left blank if there is another area element in the same image map that points to the same resource and has a non-blank alt attribute.

If the area element has no href attribute, then the area represented by the element cannot be selected, and the alt attribute must be omitted.

In both cases, the shape and coords attributes specify the area.

The shape attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map. Some of the keywords are non-conforming, as noted in the last column.

State	Keywords	Notes
Circle state	`circle`
Circle state	`circ`	Non-conforming
Default state	`default`
Polygon state	`poly`
Polygon state	`polygon`	Non-conforming
Rectangle state	`rect`
Rectangle state	`rectangle`	Non-conforming

The attribute may be omitted. The missing value default is the rectangle state.

The coords attribute must, if specified, contain a valid list of integers. This attribute gives the coordinates for the shape described by the shape attribute. The processing for this attribute is described as part of the image map processing model.

In the circle state, area elements must have a coords attribute present, with three integers, the last of which must be non-negative. The first integer must be the distance in CSS pixels from the left edge of the image to the center of the circle, the second integer must be the distance in CSS pixels from the top edge of the image to the center of the circle, and the third integer must be the radius of the circle, again in CSS pixels.

In the default state state, area elements must not have a coords attribute. (The area is the whole image.)

In the polygon state, area elements must have a coords attribute with at least six integers, and the number of integers must be even. Each pair of integers must represent a coordinate given as the distances from the left and the top of the image in CSS pixels respectively, and all the coordinates together must represent the points of the polygon, in order.

In the rectangle state, area elements must have a coords attribute with exactly four integers, the first of which must be less than the third, and the second of which must be less than the fourth. The four points must represent, respectively, the distance from the left edge of the image to the left side of the rectangle, the distance from the top edge to the top side, the distance from the left edge to the right side, and the distance from the top edge to the bottom side, all in CSS pixels.

When user agents allow users to follow hyperlinks created using the area element, as described in the next section, the href, target attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The target, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

The activation behavior of area elements is to run the following steps:

If the click event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the area element's target attribute is such that applying the rules for choosing a browsing context given a browsing context name, using the value of the target attribute as the browsing context name, would result in there not being a chosen browsing context, then raise an INVALID_ACCESS_ERR exception and abort these steps.
Otherwise, the user agent must follow the hyperlink created by the area element, if any.

The IDL attributes alt, coords, href, target, rel, media, hreflang, and type, each must reflect the respective content attributes of the same name.

The IDL attribute shape must reflect the shape content attribute.

The IDL attribute relList must reflect the rel content attribute.

The area element also supports the complement of URL decomposition IDL attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL decomposition IDL attributes, with the input being the result of resolving the element's href attribute relative to the element, if there is such an attribute and resolving it is successful, or the empty string otherwise; and the common setter action being the same as setting the element's href attribute to the new output value.

4.8.14 Image maps

4.8.14.1 Authoring

An image map allows geometric areas on an image to be associated with hyperlinks.

An image, in the form of an img element or an object element representing an image, may be associated with an image map (in the form of a map element) by specifying a usemap attribute on the img or object element. The usemap attribute, if specified, must be a valid hash-name reference to a map element.

Consider an image that looks as follows:

A line with four shapes in it, equally spaced: a red hollow box, a green circle, a blue triangle, and a yellow four-pointed star.

If we wanted just the colored areas to be clickable, we could do it as follows:

<p>
 Please select a shape:
 <img src="shapes.png" usemap="#shapes"
      alt="Four shapes are available: a red hollow box, a green circle, a blue triangle, and a yellow four-pointed star.">
 <map name="shapes">
  <area shape=rect coords="50,50,100,100"> <!-- the hole in the red box -->
  <area shape=rect coords="25,25,125,125" href="red.html" alt="Red box.">
  <area shape=circle coords="200,75,50" href="green.html" alt="Green circle.">
  <area shape=poly coords="325,25,262,125,388,125" href="blue.html" alt="Blue triangle.">
  <area shape=poly coords="450,25,435,60,400,75,435,90,450,125,465,90,500,75,465,60"
        href="yellow.html" alt="Yellow star.">
 </map>
</p>

4.8.14.2 Processing model

If an img element or an object element representing an image has a usemap attribute specified, user agents must process it as follows:

First, rules for parsing a hash-name reference to a map element must be followed. This will return either an element (the map) or null.
If that returned null, then abort these steps. The image is not associated with an image map after all.
Otherwise, the user agent must collect all the area elements that are descendants of the map. Let those be the areas.

Having obtained the list of area elements that form the image map (the areas), interactive user agents must process the list in one of two ways.

If the user agent intends to show the text that the img element represents, then it must use the following steps.

In user agents that do not support images, or that have images disabled, object elements cannot represent images, and thus this section never applies (the fallback content is shown instead). The following steps therefore only apply to img elements.

Remove all the area elements in areas that have no href attribute.
Remove all the area elements in areas that have no alt attribute, or whose alt attribute's value is the empty string, if there is another area element in areas with the same value in the href attribute and with a non-empty alt attribute.
Each remaining area element in areas represents a hyperlink. Those hyperlinks should all be made available to the user in a manner associated with the text of the img.

In this context, user agents may represent area and img elements with no specified alt attributes, or whose alt attributes are the empty string or some other non-visible text, in a user-agent-defined fashion intended to indicate the lack of suitable author-provided text.

If the user agent intends to show the image and allow interaction with the image to select hyperlinks, then the image must be associated with a set of layered shapes, taken from the area elements in areas, in reverse tree order (so the last specified area element in the map is the bottom-most shape, and the first element in the map, in tree order, is the top-most shape).

Each area element in areas must be processed as follows to obtain a shape to layer onto the image:

Find the state that the element's shape attribute represents.
Use the rules for parsing a list of integers to parse the element's coords attribute, if it is present, and let the result be the coords list. If the attribute is absent, let the coords list be the empty list.
If the number of items in the coords list is less than the minimum number given for the area element's current state, as per the following table, then the shape is empty; abort these steps.

State Minimum number of items
Circle state 3
Default state 0
Polygon state 6
Rectangle state 4
Check for excess items in the coords list as per the entry in the following list corresponding to the shape attribute's state:

Circle state

Drop any items in the list beyond the third.

Default state

Drop all items in the list.

Polygon state

Drop the last item if there's an odd number of items.

Rectangle state

Drop any items in the list beyond the fourth.
If the shape attribute represents the rectangle state, and the first number in the list is numerically less than the third number in the list, then swap those two numbers around.
If the shape attribute represents the rectangle state, and the second number in the list is numerically less than the fourth number in the list, then swap those two numbers around.
If the shape attribute represents the circle state, and the third number in the list is less than or equal to zero, then the shape is empty; abort these steps.
Now, the shape represented by the element is the one described for the entry in the list below corresponding to the state of the shape attribute:

Circle state

Let x be the first number in coords, y be the second number, and r be the third number.

The shape is a circle whose center is x CSS pixels from the left edge of the image and y CSS pixels from the top edge of the image, and whose radius is r pixels.

Default state

The shape is a rectangle that exactly covers the entire image.

Polygon state

Let x_i be the (2i)th entry in coords, and y_i be the (2i+1)th entry in coords (the first entry in coords being the one with index 0).

Let the coordinates be (x_i, y_i), interpreted in CSS pixels measured from the top left of the image, for all integer values of i from 0 to (N/2)-1, where N is the number of items in coords.

The shape is a polygon whose vertices are given by the coordinates, and whose interior is established using the even-odd rule. [GRAPHICS]

Rectangle state

Let x₁ be the first number in coords, y₁ be the second number, x₂ be the third number, and y₂ be the fourth number.

The shape is a rectangle whose top-left corner is given by the coordinate (x₁, y₁) and whose bottom right corner is given by the coordinate (x₂, y₂), those coordinates being interpreted as CSS pixels from the top left corner of the image.

For historical reasons, the coordinates must be interpreted relative to the displayed image, even if it stretched using CSS or the image element's width and height attributes.

State	Minimum number of items
Circle state	3
Default state	0
Polygon state	6
Rectangle state	4

Mouse clicks on an image associated with a set of layered shapes per the above algorithm must be dispatched to the top-most shape covering the point that the pointing device indicated (if any), and then, must be dispatched again (with a new Event object) to the image element itself. User agents may also allow individual area elements representing hyperlinks to be selected and activated (e.g. using a keyboard); events from this are not also propagated to the image.

Because a map element (and its area elements) can be associated with multiple img and object elements, it is possible for an area element to correspond to multiple focusable areas of the document.

Image maps are live; if the DOM is mutated, then the user agent must act as if it had rerun the algorithms for image maps.

4.8.15 MathML

The math element from the MathML namespace falls into the embedded content, phrasing content, and flow content categories for the purposes of the content models in this specification.

User agents must handle text other than inter-element whitespace found in MathML elements whose content models do not allow straight text by pretending for the purposes of MathML content models, layout, and rendering that that text is actually wrapped in an mtext element in the MathML namespace. (Such text is not, however, conforming.)

User agents must act as if any MathML element whose contents does not match the element's content model was replaced, for the purposes of MathML layout and rendering, by an merror element in the MathML namespace containing some appropriate error message.

To enable authors to use MathML tools that only accept MathML in its XML form, interactive HTML user agents are encouraged to provide a way to export any MathML fragment as an XML namespace-well-formed XML fragment.

The semantics of MathML elements are defined by the MathML specification and other applicable specifications. [MATHML]

Here is an example of the use of MathML in an HTML document:

<!DOCTYPE html>
<html>
 <head>
  <title>The quadratic formula</title>
 </head>
 <body>
  <h1>The quadratic formula</h1>
  <p>
   <math>
    <mi>x</mi>
    <mo>=</mo>
    <mfrac>
     <mrow>
      <mo form="prefix">−</mo> <mi>b</mi>
      <mo>±</mo>
      <msqrt>
       <msup> <mi>b</mi> <mn>2</mn> </msup>
       <mo>−</mo>
       <mn>4</mn> <mo>⁢</mo> <mi>a</mi> <mo>⁢</mo> <mi>c</mi>
      </msqrt>
     </mrow>
     <mrow>
      <mn>2</mn> <mo>⁢</mo> <mi>a</mi>
     </mrow>
    </mfrac>
   </math>
  </p>
 </body>
</html>

4.8.16 SVG

The svg element from the SVG namespace falls into the embedded content, phrasing content, and flow content categories for the purposes of the content models in this specification.

To enable authors to use SVG tools that only accept SVG in its XML form, interactive HTML user agents are encouraged to provide a way to export any SVG fragment as an XML namespace-well-formed XML fragment.

When the SVG foreignObject element contains elements from the HTML namespace, such elements must all be flow content. [SVG]

The content model for title elements in the SVG namespace inside HTML documents is phrasing content. (This further constrains the requirements given in the SVG specification.)

The semantics of SVG elements are defined by the SVG specification and other applicable specifications. [SVG]

The SVG specification includes requirements regarding the handling of elements in the DOM that are not in the SVG namespace, that are in SVG fragments, and that are not included in a foreignObject element. This specification does not define any processing for elements in SVG fragments that are not in the HTML namespace; they are considered neither conforming nor non-conforming from the perspective of this specification.

4.8.17 Dimension attributes

Author requirements: The width and height attributes on img, iframe, embed, object, video, and, when their type attribute is in the Image Button state, input elements may be specified to give the dimensions of the visual content of the element (the width and height respectively, relative to the nominal direction of the output medium), in CSS pixels. The attributes, if specified, must have values that are valid non-negative integers.

The specified dimensions given may differ from the dimensions specified in the resource itself, since the resource may have a resolution that differs from the CSS pixel resolution. (On screens, CSS pixels have a resolution of 96ppi, but in general the CSS pixel resolution depends on the reading distance.) If both attributes are specified, then one of the following statements must be true:

specified width - 0.5 ≤ specified height * target ratio ≤ specified width + 0.5
specified height - 0.5 ≤ specified width / target ratio ≤ specified height + 0.5
specified height = specified width = 0

The target ratio is the ratio of the intrinsic width to the intrinsic height in the resource. The specified width and specified height are the values of the width and height attributes respectively.

The two attributes must be omitted if the resource in question does not have both an intrinsic width and an intrinsic height.

If the two attributes are both zero, it indicates that the element is not intended for the user (e.g. it might be a part of a service to count page views).

The dimension attributes are not intended to be used to stretch the image.

User agent requirements: User agents are expected to use these attributes as hints for the rendering.

The width and height IDL attributes on the iframe, embed, object, and video elements must reflect the respective content attributes of the same name.

For iframe, embed, and object the IDL attributes are DOMString; for video the IDL attributes are unsigned long.

4.9 Tabular data

4.9.1 The `table` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

In this order: optionally a caption element, followed by zero or more colgroup elements, followed optionally by a thead element, followed optionally by a tfoot element, followed by either zero or more tbody elements or one or more tr elements, followed optionally by a tfoot element (but there can only be one tfoot element child in total).

Content attributes:

border

DOM interface:

interface HTMLTableElement : HTMLElement {
           attribute HTMLTableCaptionElement caption;
  HTMLElement createCaption();
  void deleteCaption();
           attribute HTMLTableSectionElement tHead;
  HTMLElement createTHead();
  void deleteTHead();
           attribute HTMLTableSectionElement tFoot;
  HTMLElement createTFoot();
  void deleteTFoot();
  readonly attribute HTMLCollection tBodies;
  HTMLElement createTBody();
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow(in optional long index);
  void deleteRow(in long index);
           attribute DOMString border;
};

The table element represents data with more than one dimension, in the form of a table.

The table element takes part in the table model.

Tables have rows, columns, and cells given by their descendants. The rows and columns form a grid; a table's cells must completely cover that grid without overlap.

Precise rules for determining whether this conformance requirement is met are described in the description of the table model.

Authors are encouraged to provide information describing how to interpret complex tables. Guidance on how provide such information is given below.

If a table element has a summary attribute, and the user agent has not classified the table as a layout table, the user agent may report the contents of that attribute to the user.

Tables should not be used as layout aids. Historically, many Web authors have tables in HTML as a way to control their page layout making it difficult to extract tabular data from such documents. In particular, users of accessibility tools, like screen readers, are likely to find it very difficult to navigate pages with tables used for layout. If a table is to be used for layout it must be marked with the attribute role="presentation" for a user agent to properly represent the table to an assistive technology and to properly convey the intent of the author to tools that wish to extract tabular data from the document.

There are a variety of alternatives to using HTML tables for layout, primarily using CSS positioning and the CSS table model.

The border attribute may be specified on a table element to explicitly indicate that the table element is not being used for layout purposes. If specified, the attribute's value must either be the empty string or the value "1". The attribute is used by certain user agents as an indication that borders should be drawn around cells of the table.

Tables can be complicated to understand and navigate. To help users with this, user agents should clearly dilineate cells in a table from each other, unless the user agent has classified the table as a layout table.

Authors and implementors are encouraged to consider using some of the table layout techniques described below to make tables easier to navigate for users.

User agents, especially those that do table analysis on arbitrary content, are encouraged to find heuristics to determine which tables actually contain data and which are merely being used for layout. This specification does not define a precise heuristic, but the following are suggested as possible indicators:

Feature	Indication
The use of the `role` attribute with the value `presentation`	Probably a layout table
The use of the `border` attribute with the non-conforming value 0	Probably a layout table
The use of the non-conforming `cellspacing` and `cellpadding` attributes with the value 0	Probably a layout table
The use of `caption`, `thead`, or `th` elements	Probably a non-layout table
The use of the `headers` and `scope` attributes	Probably a non-layout table
The use of the `border` attribute with a value other than 0	Probably a non-layout table
Explicit visible borders set using CSS	Probably a non-layout table
The use of the `summary` attribute	Not a good indicator (both layout and non-layout tables have historically been given this attribute)

table . caption [ = value ]

Returns the table's caption element.

Can be set, to replace the caption element. If the new value is not a caption element, throws a HIERARCHY_REQUEST_ERR exception.

caption = table . createCaption()

Ensures the table has a caption element, and returns it.

table . deleteCaption()

Ensures the table does not have a caption element.

table . tHead [ = value ]

Returns the table's thead element.

Can be set, to replace the thead element. If the new value is not a thead element, throws a HIERARCHY_REQUEST_ERR exception.

thead = table . createTHead()

Ensures the table has a thead element, and returns it.

table . deleteTHead()

Ensures the table does not have a thead element.

table . tFoot [ = value ]

Returns the table's tfoot element.

Can be set, to replace the tfoot element. If the new value is not a tfoot element, throws a HIERARCHY_REQUEST_ERR exception.

tfoot = table . createTFoot()

Ensures the table has a tfoot element, and returns it.

table . deleteTFoot()

Ensures the table does not have a tfoot element.

table . tBodies

Returns an HTMLCollection of the tbody elements of the table.

tbody = table . createTBody()

Creates a tbody element, inserts it into the table, and returns it.

table . rows

Returns an HTMLCollection of the tr elements of the table.

tr = table . insertRow(index)

Creates a tr element, along with a tbody if required, inserts them into the table at the position given by the argument, and returns the tr.

The position is relative to the rows in the table. The index −1 is equivalent to inserting at the end of the table.

If the given position is less than −1 or greater than the number of rows, throws an INDEX_SIZE_ERR exception.

table . deleteRow(index)

Removes the tr element with the given position in the table.

The position is relative to the rows in the table. The index −1 is equivalent to deleting the last row of the table.

If the given position is less than −1 or greater than the index of the last row, or if there are no rows, throws an INDEX_SIZE_ERR exception.

The caption IDL attribute must return, on getting, the first caption element child of the table element, if any, or null otherwise. On setting, if the new value is a caption element, the first caption element child of the table element, if any, must be removed, and the new value must be inserted as the first node of the table element. If the new value is not a caption element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createCaption() method must return the first caption element child of the table element, if any; otherwise a new caption element must be created, inserted as the first node of the table element, and then returned.

The deleteCaption() method must remove the first caption element child of the table element, if any.

The tHead IDL attribute must return, on getting, the first thead element child of the table element, if any, or null otherwise. On setting, if the new value is a thead element, the first thead element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table if there are no such elements. If the new value is not a thead element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTHead() method must return the first thead element child of the table element, if any; otherwise a new thead element must be created and inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table if there are no such elements, and then that new element must be returned.

The deleteTHead() method must remove the first thead element child of the table element, if any.

The tFoot IDL attribute must return, on getting, the first tfoot element child of the table element, if any, or null otherwise. On setting, if the new value is a tfoot element, the first tfoot element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements. If the new value is not a tfoot element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTFoot() method must return the first tfoot element child of the table element, if any; otherwise a new tfoot element must be created and inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements, and then that new element must be returned.

The deleteTFoot() method must remove the first tfoot element child of the table element, if any.

The tBodies attribute must return an HTMLCollection rooted at the table node, whose filter matches only tbody elements that are children of the table element.

The createTBody() method must create a new tbody element, insert it immediately after the last tbody element in the table element, if any, or at the end of the table element if the table element has no tbody element children, and then must return the new tbody element.

The rows attribute must return an HTMLCollection rooted at the table node, whose filter matches only tr elements that are either children of the table element, or children of thead, tbody, or tfoot elements that are themselves children of the table element. The elements in the collection must be ordered such that those elements whose parent is a thead are included first, in tree order, followed by those elements whose parent is either a table or tbody element, again in tree order, followed finally by those elements whose parent is a tfoot element, still in tree order.

The behavior of the insertRow(index) method depends on the state of the table. When it is called, the method must act as required by the first item in the following list of conditions that describes the state of the table and the index argument:

If index is less than −1 or greater than the number of elements in rows collection:: The method must raise an INDEX_SIZE_ERR exception.
If the rows collection has zero elements in it, and the table has no tbody elements in it:: The method must create a tbody element, then create a tr element, then append the tr element to the tbody element, then append the tbody element to the table element, and finally return the tr element.
If the rows collection has zero elements in it:: The method must create a tr element, append it to the last tbody element in the table, and return the tr element.
If index is missing, equal to −1, or equal to the number of items in rows collection:: The method must create a tr element, and append it to the parent of the last tr element in the rows collection. Then, the newly created tr element must be returned.
Otherwise:: The method must create a tr element, insert it immediately before the indexth tr element in the rows collection, in the same parent, and finally must return the newly created tr element.

When the deleteRow(index) method is called, the user agent must run the following steps:

If index is equal to −1, then index must be set to the number if items in the rows collection, minus one.
Now, if index is less than zero, or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception, and these steps must be aborted.
Otherwise, the method must remove the indexth element in the rows collection from its parent.

The border IDL attribute must reflect the content attribute of the same name.

Here is an example of a table being used to mark up a Sudoku puzzle. Observe the lack of headers, which are not necessary in such a table.

<section>
 <style scoped>
  table { border-collapse: collapse; border: solid thick; }
  colgroup, tbody { border: solid medium; }
  td { border: solid thin; height: 1.4em; width: 1.4em; text-align: center; padding: 0; }
 </style>
 <h1>Today's Sudoku</h1>
 <table>
  <colgroup><col><col><col>
  <colgroup><col><col><col>
  <colgroup><col><col><col>
  <tbody>
   <tr> <td> 1 <td>   <td> 3 <td> 6 <td>   <td> 4 <td> 7 <td>   <td> 9
   <tr> <td>   <td> 2 <td>   <td>   <td> 9 <td>   <td>   <td> 1 <td>
   <tr> <td> 7 <td>   <td>   <td>   <td>   <td>   <td>   <td>   <td> 6
  <tbody>
   <tr> <td> 2 <td>   <td> 4 <td>   <td> 3 <td>   <td> 9 <td>   <td> 8
   <tr> <td>   <td>   <td>   <td>   <td>   <td>   <td>   <td>   <td>
   <tr> <td> 5 <td>   <td>   <td> 9 <td>   <td> 7 <td>   <td>   <td> 1
  <tbody>
   <tr> <td> 6 <td>   <td>   <td>   <td> 5 <td>   <td>   <td>   <td> 2
   <tr> <td>   <td>   <td>   <td>   <td> 7 <td>   <td>   <td>   <td>
   <tr> <td> 9 <td>   <td>   <td> 8 <td>   <td> 2 <td>   <td>   <td> 5
 </table>
</section>

4.9.1.1 Techniques for describing tables

For tables that consist of more than just a grid of cells with headers in the first row and headers in the first column, and for any table in general where the reader might have difficulty understanding the content, authors should include explanatory information introducing the table. This information is useful for all users, but is especially useful for users who cannot see the table, e.g. users of screen readers.

Such explanatory information should introduce the purpose of the table, outline its basic cell structure, highlight any trends or patterns, and generally teach the user how to use the table.

For instance, the following table:

Characteristics with positive and negative sides
Negative	Characteristic	Positive
Sad	Mood	Happy
Failing	Grade	Passing

...might benefit from a description explaining the way the table is laid out, something like "Characteristics are given in the second column, with the negative side in the left column and the positive side in the right column".

There are a variety of ways to include this information, such as:

In prose, surrounding the table

<p>In the following table, characteristics are given in the second
column, with the negative side in the left column and the positive
side in the right column.</p>
<table>
 <caption>Characteristics with positive and negative sides</caption>
 <thead>
  <tr>
   <th id="n"> Negative
   <th> Characteristic
   <th> Positive
 <tbody>
  <tr>
   <td headers="n r1"> Sad
   <th id="r1"> Mood
   <td> Happy
  <tr>
   <td headers="n r2"> Failing
   <th id="r2"> Grade
   <td> Passing
</table>

In the table's caption

<table>
 <caption>
  <strong>Characteristics with positive and negative sides.</strong>
  <p>Characteristics are given in the second column, with the
  negative side in the left column and the positive side in the right
  column.</p>
 </caption>
 <thead>
  <tr>
   <th id="n"> Negative
   <th> Characteristic
   <th> Positive
 <tbody>
  <tr>
   <td headers="n r1"> Sad
   <th id="r1"> Mood
   <td> Happy
  <tr>
   <td headers="n r2"> Failing
   <th id="r2"> Grade
   <td> Passing
</table>

In the table's caption, in a details element

<table>
 <caption>
  <strong>Characteristics with positive and negative sides.</strong>
  <details>
   <summary>Help</summary>
   <p>Characteristics are given in the second column, with the
   negative side in the left column and the positive side in the right
   column.</p>
  </details>
 </caption>
 <thead>
  <tr>
   <th id="n"> Negative
   <th> Characteristic
   <th> Positive
 <tbody>
  <tr>
   <td headers="n r1"> Sad
   <th id="r1"> Mood
   <td> Happy
  <tr>
   <td headers="n r2"> Failing
   <th id="r2"> Grade
   <td> Passing
</table>

Next to the table, in the same figure

<figure>
 <figcaption>Characteristics with positive and negative sides</figcaption>
 <p>Characteristics are given in the second column, with the
 negative side in the left column and the positive side in the right
 column.</p>
 <table>
  <thead>
   <tr>
    <th id="n"> Negative
    <th> Characteristic
    <th> Positive
  <tbody>
   <tr>
    <td headers="n r1"> Sad
    <th id="r1"> Mood
    <td> Happy
   <tr>
    <td headers="n r2"> Failing
    <th id="r2"> Grade
    <td> Passing
 </table>
</figure>

Next to the table, in a figure's figcaption

<figure>
 <figcaption>
  <strong>Characteristics with positive and negative sides</strong>
  <p>Characteristics are given in the second column, with the
  negative side in the left column and the positive side in the right
  column.</p>
 </figcaption>
 <table>
  <thead>
   <tr>
    <th id="n"> Negative
    <th> Characteristic
    <th> Positive
  <tbody>
   <tr>
    <td headers="n r1"> Sad
    <th id="r1"> Mood
    <td> Happy
   <tr>
    <td headers="n r2"> Failing
    <th id="r2"> Grade
    <td> Passing
 </table>
</figure>

Authors may also use other techniques, or combinations of the above techniques, as appropriate.

The best option, of course, rather than writing a description explaining the way the table is laid out, is to adjust the table such that no explanation is needed.

In the case of the table used in the examples above, a simple rearrangement of the table so that the headers are on the top and left sides removes the need for an explanation as well as removing the need for the use of headers attributes:

<table>
 <caption>Characteristics with positive and negative sides</caption>
 <thead>
  <tr>
   <th> Characteristic
   <th> Negative
   <th> Positive
 <tbody>
  <tr>
   <th> Mood
   <td> Sad
   <td> Happy
  <tr>
   <th> Grade
   <td> Failing
   <td> Passing
</table>

4.9.1.2 Techniques for table layout

Good table layout is key to making tables more readable and usable.

In visual media, providing column and row borders and alternating row backgrounds can be very effective to make complicated tables more readable.

For tables with large volumes of numeric content, using monospaced fonts can help users see patterns, especially in situations where a user agent does not render the borders. (Unfortunately, for historical reasons, not rendering borders on tables is a common default.)

In speech media, table cells can be distinguished by reporting the corresponding headers before reading the cell's contents, and by allowing users to navigate the table in a grid fashion, rather than serializing the entire contents of the table in source order.

Authors are encouraged to use CSS to achieve these effects.

User agents are encouraged to render tables using these techniques whenever the page does not use CSS and the table is not classified as a layout table.

4.9.2 The `caption` element

Categories

None.

Contexts in which this element can be used:

As the first element child of a table element.

Content model:

Flow content, but with no descendant table elements.

Content attributes:

DOM interface:

interface HTMLTableCaptionElement : HTMLElement {};

The caption element represents the title of the table that is its parent, if it has a parent and that is a table element.

The caption element takes part in the table model.

When a table element is the only content in a figure element other than the figcaption, the caption element should be omitted in favor of the figcaption.

A caption can introduce context for a table, making it significantly easier to understand.

Consider, for instance, the following table:

	1	2	3	4	5	6
1	2	3	4	5	6	7
2	3	4	5	6	7	8
3	4	5	6	7	8	9
4	5	6	7	8	9	10
5	6	7	8	9	10	11
6	7	8	9	10	11	12

In the abstract, this table is not clear. However, with a caption giving the table's number (for reference in the main prose) and explaining its use, it makes more sense:

<caption>
<p>Table 1.
<p>This table shows the total score obtained from rolling two
six-sided dice. The first row represents the value of the first die,
the first column the value of the second die. The total is given in
the cell that corresponds to the values of the two dice.
</caption>

4.9.3 The `colgroup` element

Categories

None.

Contexts in which this element can be used:

As a child of a table element, after any caption elements and before any thead, tbody, tfoot, and tr elements.

Content model:

If the span attribute is present: Empty.

If the span attribute is absent: Zero or more col elements.

Content attributes:

span

DOM interface:

interface HTMLTableColElement : HTMLElement {
           attribute unsigned long span;
};

The colgroup element represents a group of one or more columns in the table that is its parent, if it has a parent and that is a table element.

If the colgroup element contains no col elements, then the element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The colgroup element and its span attribute take part in the table model.

The span IDL attribute must reflect the content attribute of the same name. The value must be limited to only non-negative numbers greater than zero.

4.9.4 The `col` element

Categories: None.
Contexts in which this element can be used:: As a child of a colgroup element that doesn't have a span attribute.
Content model:: Empty.
Content attributes:: Global attributes; span
DOM interface:: HTMLTableColElement, same as for colgroup elements. This interface defines one member, span.

If a col element has a parent and that is a colgroup element that itself has a parent that is a table element, then the col element represents one or more columns in the column group represented by that colgroup.

The element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The col element and its span attribute take part in the table model.

The span IDL attribute must reflect the content attribute of the same name. The value must be limited to only non-negative numbers greater than zero.

4.9.5 The `tbody` element

Categories

None.

Contexts in which this element can be used:

As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tr elements that are children of the table element.

Content model:

Zero or more tr elements

Content attributes:

DOM interface:

interface HTMLTableSectionElement : HTMLElement {
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow(in optional long index);
  void deleteRow(in long index);
};

The HTMLTableSectionElement interface is also used for thead and tfoot elements.

The tbody element represents a block of rows that consist of a body of data for the parent table element, if the tbody element has a parent and it is a table.

The tbody element takes part in the table model.

tbody . rows

Returns an HTMLCollection of the tr elements of the table section.

tr = tbody . insertRow( [ index ] )

Creates a tr element, inserts it into the table section at the position given by the argument, and returns the tr.

The position is relative to the rows in the table section. The index −1, which is the default if the argument is omitted, is equivalent to inserting at the end of the table section.

If the given position is less than −1 or greater than the number of rows, throws an INDEX_SIZE_ERR exception.

tbody . deleteRow(index)

Removes the tr element with the given position in the table section.

The position is relative to the rows in the table section. The index −1 is equivalent to deleting the last row of the table section.

If the given position is less than −1 or greater than the index of the last row, or if there are no rows, throws an INDEX_SIZE_ERR exception.

The rows attribute must return an HTMLCollection rooted at the element, whose filter matches only tr elements that are children of the element.

The insertRow(index) method must, when invoked on an element table section, act as follows:

If index is less than −1 or greater than the number of elements in the rows collection, the method must raise an INDEX_SIZE_ERR exception.

If index is missing, equal to −1, or equal to the number of items in the rows collection, the method must create a tr element, append it to the element table section, and return the newly created tr element.

Otherwise, the method must create a tr element, insert it as a child of the table section element, immediately before the indexth tr element in the rows collection, and finally must return the newly created tr element.

The deleteRow(index) method must remove the indexth element in the rows collection from its parent. If index is less than zero or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception.

4.9.6 The `thead` element

Categories: None.
Contexts in which this element can be used:: As a child of a table element, after any caption, and colgroup elements and before any tbody, tfoot, and tr elements, but only if there are no other thead elements that are children of the table element.
Content model:: Zero or more tr elements
Content attributes:: Global attributes
DOM interface:: HTMLTableSectionElement, as defined for tbody elements.

The thead element represents the block of rows that consist of the column labels (headers) for the parent table element, if the thead element has a parent and it is a table.

The thead element takes part in the table model.

This example shows a thead element being used. Notice the use of both th and td elements in the thead element: the first row is the headers, and the second row is an explanation of how to fill in the table.

<table>
 <caption> School auction sign-up sheet </caption>
 <thead>
  <tr>
   <th><label for=e1>Name</label>
   <th><label for=e2>Product</label>
   <th><label for=e3>Picture</label>
   <th><label for=e4>Price</label>
  <tr>
   <td>Your name here
   <td>What are you selling?
   <td>Link to a picture
   <td>Your reserve price
 <tbody>
  <tr>
   <td>Ms Danus
   <td>Doughnuts
   <td><img src="http://example.com/mydoughnuts.png" title="Doughnuts from Ms Danus">
   <td>$45
  <tr>
   <td><input id=e1 type=text name=who required form=f>
   <td><input id=e2 type=text name=what required form=f>
   <td><input id=e3 type=url name=pic form=f>
   <td><input id=e4 type=number step=0.01 min=0 value=0 required form=f>
</table>
<form id=f action="/auction.cgi">
 <input type=button name=add value="Submit">
</form>

4.9.7 The `tfoot` element

Categories: None.
Contexts in which this element can be used:: As a child of a table element, after any caption, colgroup, and thead elements and before any tbody and tr elements, but only if there are no other tfoot elements that are children of the table element.; As a child of a table element, after any caption, colgroup, thead, tbody, and tr elements, but only if there are no other tfoot elements that are children of the table element.
Content model:: Zero or more tr elements
Content attributes:: Global attributes
DOM interface:: HTMLTableSectionElement, as defined for tbody elements.

The tfoot element represents the block of rows that consist of the column summaries (footers) for the parent table element, if the tfoot element has a parent and it is a table.

The tfoot element takes part in the table model.

4.9.8 The `tr` element

Categories

None.

Contexts in which this element can be used:

As a child of a thead element.

As a child of a tbody element.

As a child of a tfoot element.

As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tbody elements that are children of the table element.

Content model:

Zero or more td or th elements

Content attributes:

DOM interface:

interface HTMLTableRowElement : HTMLElement {
  readonly attribute long rowIndex;
  readonly attribute long sectionRowIndex;
  readonly attribute HTMLCollection cells;
  HTMLElement insertCell(in optional long index);
  void deleteCell(in long index);
};

The tr element represents a row of cells in a table.

The tr element takes part in the table model.

tr . rowIndex

Returns the position of the row in the table's rows list.

Returns −1 if the element isn't in a table.

tr . sectionRowIndex

Returns the position of the row in the table section's rows list.

Returns −1 if the element isn't in a table section.

tr . cells

Returns an HTMLCollection of the td and th elements of the row.

cell = tr . insertCell( [ index ] )

Creates a td element, inserts it into the table row at the position given by the argument, and returns the td.

The position is relative to the cells in the row. The index −1, which is the default if the argument is omitted, is equivalent to inserting at the end of the row.

If the given position is less than −1 or greater than the number of cells, throws an INDEX_SIZE_ERR exception.

tr . deleteCell(index)

Removes the td or th element with the given position in the row.

The position is relative to the cells in the row. The index −1 is equivalent to deleting the last cell of the row.

If the given position is less than −1 or greater than the index of the last cell, or if there are no cells, throws an INDEX_SIZE_ERR exception.

The rowIndex attribute must, if the element has a parent table element, or a parent tbody, thead, or tfoot element and a grandparent table element, return the index of the tr element in that table element's rows collection. If there is no such table element, then the attribute must return −1.

The sectionRowIndex attribute must, if the element has a parent table, tbody, thead, or tfoot element, return the index of the tr element in the parent element's rows collection (for tables, that's the HTMLTableElement.rows collection; for table sections, that's the HTMLTableRowElement.rows collection). If there is no such parent element, then the attribute must return −1.

The cells attribute must return an HTMLCollection rooted at the tr element, whose filter matches only td and th elements that are children of the tr element.

The insertCell(index) method must act as follows:

If index is less than −1 or greater than the number of elements in the cells collection, the method must raise an INDEX_SIZE_ERR exception.

If index is missing, equal to −1, or equal to the number of items in cells collection, the method must create a td element, append it to the tr element, and return the newly created td element.

Otherwise, the method must create a td element, insert it as a child of the tr element, immediately before the indexth td or th element in the cells collection, and finally must return the newly created td element.

The deleteCell(index) method must remove the indexth element in the cells collection from its parent. If index is less than zero or greater than or equal to the number of elements in the cells collection, the method must instead raise an INDEX_SIZE_ERR exception.

4.9.9 The `td` element

Categories

Contexts in which this element can be used:

As a child of a tr element.

Content model:

Content attributes:

colspan

rowspan

headers

DOM interface:

interface HTMLTableDataCellElement : HTMLTableCellElement {};

The td element represents a data cell in a table.

The td element and its colspan, rowspan, and headers attributes take part in the table model.

4.9.10 The `th` element

Categories

None.

Contexts in which this element can be used:

As a child of a tr element.

Content model:

Content attributes:

colspan

rowspan

headers

scope

DOM interface:

interface HTMLTableHeaderCellElement : HTMLTableCellElement {
           attribute DOMString scope;
};

The th element represents a header cell in a table.

The th element may have a scope content attribute specified. The scope attribute is an enumerated attribute with five states, four of which have explicit keywords:

The row keyword, which maps to the row state: The row state means the header cell applies to some of the subsequent cells in the same row(s).
The col keyword, which maps to the column state: The column state means the header cell applies to some of the subsequent cells in the same column(s).
The rowgroup keyword, which maps to the row group state: The row group state means the header cell applies to all the remaining cells in the row group. A th element's scope attribute must not be in the row group state if the element is not anchored in a row group.
The colgroup keyword, which maps to the column group state: The column group state means the header cell applies to all the remaining cells in the column group. A th element's scope attribute must not be in the column group state if the element is not anchored in a column group.
The auto state: The auto state makes the header cell apply to a set of cells selected based on context.

The scope attribute's missing value default is the auto state.

The th element and its colspan, rowspan, headers, and scope attributes take part in the table model.

The scope IDL attribute must reflect the content attribute of the same name, limited to only known values.

The following example shows how the scope attribute's rowgroup value affects which data cells a header cell applies to.

Here is a markup fragment showing a table:

<table>
 <thead>
  <tr> <th> ID <th> Measurement <th> Average <th> Maximum
 <tbody>
  <tr> <td> <th scope=rowgroup> Cats <td> <td>
  <tr> <td> 93 <th scope=row> Legs <td> 3.5 <td> 4
  <tr> <td> 10 <th scope=row> Tails <td> 1 <td> 1
 <tbody>
  <tr> <td> <th scope=rowgroup> English speakers <td> <td>
  <tr> <td> 32 <th scope=row> Legs <td> 2.67 <td> 4
  <tr> <td> 35 <th scope=row> Tails <td> 0.33 <td> 1
</table>

This would result in the following table:

ID	Measurement	Average	Maximum
	Cats
93	Legs	3.5	4
10	Tails	1	1
	English speakers
32	Legs	2.67	4
35	Tails	0.33	1

The headers in the first row all apply directly down to the rows in their column.

The headers with the explicit scope attributes apply to all the cells in their row group other than the cells in the first column.

The remaining headers apply just to the cells to the right of them.

4.9.11 Attributes common to `td` and `th` elements

The td and th elements may have a colspan content attribute specified, whose value must be a valid non-negative integer greater than zero.

The td and th elements may also have a rowspan content attribute specified, whose value must be a valid non-negative integer.

These attributes give the number of columns and rows respectively that the cell is to span. These attributes must not be used to overlap cells, as described in the description of the table model.

The td and th element may have a headers content attribute specified. The headers attribute, if specified, must contain a string consisting of an unordered set of unique space-separated tokens that are case-sensitive, each of which must have the value of an ID of a th element taking part in the same table as the td or th element (as defined by the table model).

A th element with ID id is said to be directly targeted by all td and th elements in the same table that have headers attributes whose values include as one of their tokens the ID id. A th element A is said to be targeted by a th or td element B if either A is directly targeted by B or if there exists an element C that is itself targeted by the element B and A is directly targeted by C.

A th element must not be targeted by itself.

The colspan, rowspan, and headers attributes take part in the table model.

The td and th elements implement interfaces that inherit from the HTMLTableCellElement interface:

interface HTMLTableCellElement : HTMLElement {
           attribute unsigned long colSpan;
           attribute unsigned long rowSpan;
  [PutForwards=value] readonly attribute DOMSettableTokenList headers;
  readonly attribute long cellIndex;
};

cell . cellIndex

Returns the position of the cell in the row's cells list. This does not necessarily correspond to the x-position of the cell in the table, since earlier cells might cover multiple rows or columns.

Returns 0 if the element isn't in a row.

The colSpan IDL attribute must reflect the content attribute of the same name. The value must be limited to only non-negative numbers greater than zero.

The rowSpan IDL attribute must reflect the content attribute of the same name. Its default value, which must be used if parsing the attribute as a non-negative integer returns an error, is 1.

The headers IDL attribute must reflect the content attribute of the same name.

The cellIndex IDL attribute must, if the element has a parent tr element, return the index of the cell's element in the parent element's cells collection. If there is no such parent element, then the attribute must return 0.

4.9.12 Processing model

The various table elements and their content attributes together define the table model.

A table consists of cells aligned on a two-dimensional grid of slots with coordinates (x, y). The grid is finite, and is either empty or has one or more slots. If the grid has one or more slots, then the x coordinates are always in the range 0 ≤ x < x_width, and the y coordinates are always in the range 0 ≤ y < y_height. If one or both of x_width and y_height are zero, then the table is empty (has no slots). Tables correspond to table elements.

A cell is a set of slots anchored at a slot (cell_x, cell_y), and with a particular width and height such that the cell covers all the slots with coordinates (x, y) where cell_x ≤ x < cell_x+width and cell_y ≤ y < cell_y+height. Cells can either be data cells or header cells. Data cells correspond to td elements, and header cells correspond to th elements. Cells of both types can have zero or more associated header cells.

It is possible, in certain error cases, for two cells to occupy the same slot.

A row is a complete set of slots from x=0 to x=x_width-1, for a particular value of y. Rows correspond to tr elements.

A column is a complete set of slots from y=0 to y=y_height-1, for a particular value of x. Columns can correspond to col elements. In the absence of col elements, columns are implied.

A row group is a set of rows anchored at a slot (0, group_y) with a particular height such that the row group covers all the slots with coordinates (x, y) where 0 ≤ x < x_width and group_y ≤ y < group_y+height. Row groups correspond to tbody, thead, and tfoot elements. Not every row is necessarily in a row group.

A column group is a set of columns anchored at a slot (group_x, 0) with a particular width such that the column group covers all the slots with coordinates (x, y) where group_x ≤ x < group_x+width and 0 ≤ y < y_height. Column groups correspond to colgroup elements. Not every column is necessarily in a column group.

Row groups cannot overlap each other. Similarly, column groups cannot overlap each other.

A cell cannot cover slots that are from two or more row groups. It is, however, possible for a cell to be in multiple column groups. All the slots that form part of one cell are part of zero or one row groups and zero or more column groups.

In addition to cells, columns, rows, row groups, and column groups, tables can have a caption element associated with them. This gives the table a heading, or legend.

A table model error is an error with the data represented by table elements and their descendants. Documents must not have table model errors.

4.9.12.1 Forming a table

To determine which elements correspond to which slots in a table associated with a table element, to determine the dimensions of the table (x_width and y_height), and to determine if there are any table model errors, user agents must use the following algorithm:

Let x_width be zero.
Let y_height be zero.
Let pending tfoot elements be a list of tfoot elements, initially empty.
Let the table be the table represented by the table element. The x_width and y_height variables give the table's dimensions. The table is initially empty.
If the table element has no children elements, then return the table (which will be empty), and abort these steps.
Associate the first caption element child of the table element with the table. If there are no such children, then it has no associated caption element.
Let the current element be the first element child of the table element.

If a step in this algorithm ever requires the current element to be advanced to the next child of the table when there is no such next child, then the user agent must jump to the step labeled end, near the end of this algorithm.
While the current element is not one of the following elements, advance the current element to the next child of the table:
- colgroup
- thead
- tbody
- tfoot
- tr
If the current element is a colgroup, follow these substeps:
1. Column groups: Process the current element according to the appropriate case below:
  If the current element has any col element children
  Follow these steps:
  1. Let x_start have the value of x_width.
  2. Let the current column be the first col element child of the colgroup element.
  3. Columns: If the current column col element has a span attribute, then parse its value using the rules for parsing non-negative integers.
    
    If the result of parsing the value is not an error or zero, then let span be that value.
    
    Otherwise, if the col element has no span attribute, or if trying to parse the attribute's value resulted in an error or zero, then let span be 1.
  4. Increase x_width by span.
  5. Let the last span columns in the table correspond to the current column col element.
  6. If current column is not the last col element child of the colgroup element, then let the current column be the next col element child of the colgroup element, and return to the step labeled columns.
  7. Let all the last columns in the table from x=x_start to x=x_width-1 form a new column group, anchored at the slot (x_start, 0), with width x_width-x_start, corresponding to the colgroup element.
  If the current element has no col element children
  1. If the colgroup element has a span attribute, then parse its value using the rules for parsing non-negative integers.
    
    If the result of parsing the value is not an error or zero, then let span be that value.
    
    Otherwise, if the colgroup element has no span attribute, or if trying to parse the attribute's value resulted in an error or zero, then let span be 1.
  2. Increase x_width by span.
  3. Let the last span columns in the table form a new column group, anchored at the slot (x_width-span, 0), with width span, corresponding to the colgroup element.
2. Advance the current element to the next child of the table.
3. While the current element is not one of the following elements, advance the current element to the next child of the table:
  - colgroup
  - thead
  - tbody
  - tfoot
  - tr
4. If the current element is a colgroup element, jump to the step labeled column groups above.
Let y_current be zero.
Let the list of downward-growing cells be an empty list.
Rows: While the current element is not one of the following elements, advance the current element to the next child of the table:
- thead
- tbody
- tfoot
- tr
If the current element is a tr, then run the algorithm for processing rows, advance the current element to the next child of the table, and return to the step labeled rows.
Run the algorithm for ending a row group.
If the current element is a tfoot, then add that element to the list of pending tfoot elements, advance the current element to the next child of the table, and return to the step labeled rows.
The current element is either a thead or a tbody.

Run the algorithm for processing row groups.
Advance the current element to the next child of the table.
Return to the step labeled rows.
End: For each tfoot element in the list of pending tfoot elements, in tree order, run the algorithm for processing row groups.
If there exists a row or column in the table containing only slots that do not have a cell anchored to them, then this is a table model error.
Return the table.

The algorithm for processing row groups, which is invoked by the set of steps above for processing thead, tbody, and tfoot elements, is:

Let y_start have the value of y_height.
For each tr element that is a child of the element being processed, in tree order, run the algorithm for processing rows.
If y_height > y_start, then let all the last rows in the table from y=y_start to y=y_height-1 form a new row group, anchored at the slot with coordinate (0, y_start), with height y_height-y_start, corresponding to the element being processed.
Run the algorithm for ending a row group.

The algorithm for ending a row group, which is invoked by the set of steps above when starting and ending a block of rows, is:

While y_current is less than y_height, follow these steps:
1. Run the algorithm for growing downward-growing cells.
2. Increase y_current by 1.
Empty the list of downward-growing cells.

The algorithm for processing rows, which is invoked by the set of steps above for processing tr elements, is:

If y_height is equal to y_current, then increase y_height by 1. (y_current is never greater than y_height.)
Let x_current be 0.
Run the algorithm for growing downward-growing cells.
If the tr element being processed has no td or th element children, then increase y_current by 1, abort this set of steps, and return to the algorithm above.
Let current cell be the first td or th element in the tr element being processed.
Cells: While x_current is less than x_width and the slot with coordinate (x_current, y_current) already has a cell assigned to it, increase x_current by 1.
If x_current is equal to x_width, increase x_width by 1. (x_current is never greater than x_width.)
If the current cell has a colspan attribute, then parse that attribute's value, and let colspan be the result.

If parsing that value failed, or returned zero, or if the attribute is absent, then let colspan be 1, instead.
If the current cell has a rowspan attribute, then parse that attribute's value, and let rowspan be the result.

If parsing that value failed or if the attribute is absent, then let rowspan be 1, instead.
If rowspan is zero, then let cell grows downward be true, and set rowspan to 1. Otherwise, let cell grows downward be false.
If x_width < x_current+colspan, then let x_width be x_current+colspan.
If y_height < y_current+rowspan, then let y_height be y_current+rowspan.
Let the slots with coordinates (x, y) such that x_current ≤ x < x_current+colspan and y_current ≤ y < y_current+rowspan be covered by a new cell c, anchored at (x_current, y_current), which has width colspan and height rowspan, corresponding to the current cell element.

If the current cell element is a th element, let this new cell c be a header cell; otherwise, let it be a data cell.

To establish which header cells apply to the current cell element, use the algorithm for assigning header cells described in the next section.

If any of the slots involved already had a cell covering them, then this is a table model error. Those slots now have two cells overlapping.
If cell grows downward is true, then add the tuple {c, x_current, colspan} to the list of downward-growing cells.
Increase x_current by colspan.
If current cell is the last td or th element in the tr element being processed, then increase y_current by 1, abort this set of steps, and return to the algorithm above.
Let current cell be the next td or th element in the tr element being processed.
Return to the step labelled cells.

When the algorithms above require the user agent to run the algorithm for growing downward-growing cells, the user agent must, for each {cell, cell_x, width} tuple in the list of downward-growing cells, if any, extend the cell cell so that it also covers the slots with coordinates (x, y_current), where cell_x ≤ x < cell_x+width.

4.9.12.2 Forming relationships between data cells and header cells

Each cell can be assigned zero or more header cells. The algorithm for assigning header cells to a cell principal cell is as follows.

Let header list be an empty list of cells.
Let (principal_x, principal_y) be the coordinate of the slot to which the principal cell is anchored.
If the principal cell has a headers attribute specified
1. Take the value of the principal cell's headers attribute and split it on spaces, letting id list be the list of tokens obtained.
2. For each token in the id list, if the first element in the Document with an ID equal to the token is a cell in the same table, and that cell is not the principal cell, then add that cell to header list.
If principal cell does not have a headers attribute specified
1. Let principal_width be the width of the principal cell.
2. Let principal_height be the height of the principal cell.
3. For each value of y from principal_y to principal_y+principal_height-1, run the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate (principal_x,y), and the increments Δx=−1 and Δy=0.
4. For each value of x from principal_x to principal_x+principal_width-1, run the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate (x,principal_y), and the increments Δx=0 and Δy=−1.
5. If the principal cell is anchored in a row group, then add all header cells that are row group headers and are anchored in the same row group with an x-coordinate less than or equal to principal_x+principal_width-1 and a y-coordinate less than or equal to principal_y+principal_height-1 to header list.
6. If the principal cell is anchored in a column group, then add all header cells that are column group headers and are anchored in the same column group with an x-coordinate less than or equal to principal_x+principal_width-1 and a y-coordinate less than or equal to principal_y+principal_height-1 to header list.
Remove all the empty cells from the header list.
Remove any duplicates from the header list.
Remove principal cell from the header list if it is there.
Assign the headers in the header list to the principal cell.

The internal algorithm for scanning and assigning header cells, given a principal cell, a header list, an initial coordinate (initial_x, initial_y), and Δx and Δy increments, is as follows:

Let x equal initial_x.
Let y equal initial_y.
Let opaque headers be an empty list of cells.
If principal cell is a header cell

Let in header block be true, and let headers from current header block be a list of cells containing just the principal cell.

Otherwise

Let in header block be false and let headers from current header block be an empty list of cells.
Loop: Increment x by Δx; increment y by Δy.

For each invocation of this algorithm, one of Δx and Δy will be −1, and the other will be 0.
If either x or y is less than 0, then abort this internal algorithm.
If there is no cell covering slot (x, y), or if there is more than one cell covering slot (x, y), return to the substep labeled loop.
Let current cell be the cell covering slot (x, y).
If current cell is a header cell
1. Set in header block to true.
2. Add current cell to headers from current header block.
3. Let blocked be false.
4. If Δx is 0
  
  If there are any cells in the opaque headers list anchored with the same x-coordinate as the current cell, and with the same width as current cell, then let blocked be true.
  
  If the current cell is not a column header, then let blocked be true.
  
  If Δy is 0
  
  If there are any cells in the opaque headers list anchored with the same y-coordinate as the current cell, and with the same height as current cell, then let blocked be true.
  
  If the current cell is not a row header, then let blocked be true.
5. If blocked is false, then add the current cell to the headers list.
If current cell is a data cell and in header block is true

Set in header block to false. Add all the cells in headers from current header block to the opaque headers list, and empty the headers from current header block list.
Return to the step labeled loop.

A header cell anchored at the slot with coordinate (x, y) with width width and height height is said to be a column header if any of the following conditions are true:

The cell's scope attribute is in the column state, or
The cell's scope attribute is in the auto state, and there are no data cells in any of the cells covering slots with y-coordinates y .. y+height-1.

A header cell anchored at the slot with coordinate (x, y) with width width and height height is said to be a row header if any of the following conditions are true:

The cell's scope attribute is in the row state, or
The cell's scope attribute is in the auto state, the cell is not a column header, and there are no data cells in any of the cells covering slots with x-coordinates x .. x+width-1.

A header cell is said to be a column group header if its scope attribute is in the column group state.

A header cell is said to be a row group header if its scope attribute is in the row group state.

A cell is said to be an empty cell if it contains no elements and its text content, if any, consists only of White_Space characters.

4.9.13 Examples

This section is non-normative.

The following shows how might one mark up the bottom part of table 45 of the Smithsonian physical tables, Volume 71:

<table>
 <caption>Specification values: <b>Steel</b>, <b>Castings</b>,
 Ann. A.S.T.M. A27-16, Class B;* P max. 0.06; S max. 0.05.</caption>
 <thead>
  <tr>
   <th rowspan=2>Grade.</th>
   <th rowspan=2>Yield Point.</th>
   <th colspan=2>Ultimate tensile strength</th>
   <th rowspan=2>Per cent elong. 50.8mm or 2 in.</th>
   <th rowspan=2>Per cent reduct. area.</th>
  </tr>
  <tr>
   <th>kg/mm<sup>2</sup></th>
   <th>lb/in<sup>2</sup></th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>Hard</td>
   <td>0.45 ultimate</td>
   <td>56.2</td>
   <td>80,000</td>
   <td>15</td>
   <td>20</td>
  </tr>
  <tr>
   <td>Medium</td>
   <td>0.45 ultimate</td>
   <td>49.2</td>
   <td>70,000</td>
   <td>18</td>
   <td>25</td>
  </tr>
  <tr>
   <td>Soft</td>
   <td>0.45 ultimate</td>
   <td>42.2</td>
   <td>60,000</td>
   <td>22</td>
   <td>30</td>
  </tr>
 </tbody>
</table>

This table could look like this:

Specification values: **Steel**, **Castings**, Ann. A.S.T.M. A27-16, Class B;* P max. 0.06; S max. 0.05.
Grade.	Yield Point.	Ultimate tensile strength		Per cent elong. 50.8 mm or 2 in.	Per cent reduct. area.
Grade.	Yield Point.	kg/mm²	lb/in²	Per cent elong. 50.8 mm or 2 in.	Per cent reduct. area.
Hard	0.45 ultimate	56.2	80,000	15	20
Medium	0.45 ultimate	49.2	70,000	18	25
Soft	0.45 ultimate	42.2	60,000	22	30

The following shows how one might mark up the gross margin table on page 46 of Apple, Inc's 10-K filing for fiscal year 2008:

<table>
 <thead>
  <tr>
   <th>
   <th>2008
   <th>2007
   <th>2006
 <tbody>
  <tr>
   <th>Net sales
   <td>$ 32,479
   <td>$ 24,006
   <td>$ 19,315
  <tr>
   <th>Cost of sales
   <td>  21,334
   <td>  15,852
   <td>  13,717
 <tbody>
  <tr>
   <th>Gross margin
   <td>$ 11,145
   <td>$  8,154
   <td>$  5,598
 <tfoot>
  <tr>
   <th>Gross margin percentage
   <td>34.3%
   <td>34.0%
   <td>29.0%
</table>

The following shows how one might mark up the operating expenses table from lower on the same page of that document:

<table>
 <colgroup> <col>
 <colgroup> <col> <col> <col>
 <thead>
  <tr> <th> <th>2008 <th>2007 <th>2006
 <tbody>
  <tr> <th scope=rowgroup> Research and development
       <td> $ 1,109 <td> $ 782 <td> $ 712
  <tr> <th scope=row> Percentage of net sales
       <td> 3.4% <td> 3.3% <td> 3.7%
 <tbody>
  <tr> <th scope=rowgroup> Selling, general, and administrative
       <td> $ 3,761 <td> $ 2,963 <td> $ 2,433
  <tr> <th scope=row> Percentage of net sales
       <td> 11.6% <td> 12.3% <td> 12.6%
</table>

This table could look like this:

	2008	2007	2006
Research and development	$ 1,109	$ 782	$ 712
Percentage of net sales	3.4%	3.3%	3.7%
Selling, general, and administrative	$ 3,761	$ 2,963	$ 2,433
Percentage of net sales	11.6%	12.3%	12.6%

4.10 Forms

4.10.1 Introduction

This section is non-normative.

A form is a component of a Web page that has form controls, such as text fields, buttons, checkboxes, range controls, or color pickers. A user can interact with such a form, providing data that can then be sent to the server for further processing (e.g. returning the results of a search or calculation). No client-side scripting is needed in many cases, though an API is available so that scripts can augment the user experience or use forms for purposes other than submitting data to a server.

Writing a form consists of several steps, which can be performed in any order: writing the user interface, implementing the server-side processing, and configuring the user interface to communicate with the server.

4.10.1.1 Writing a form's user interface

This section is non-normative.

For the purposes of this brief introduction, we will create a pizza ordering form.

Any form starts with a form element, inside which are placed the controls. Most controls are represented by the input element, which by default provides a one-line text field. To label a control, the label element is used; the label text and the control itself go inside the label element. Each part of a form is considered a paragraph, and is typically separated from other parts using p elements. Putting this together, here is how one might ask for the customer's name:

<form>
 <p><label>Customer name: <input></label></p>
</form>

To let the user select the size of the pizza, we can use a set of radio buttons. Radio buttons also use the input element, this time with a type attribute with the value radio. To make the radio buttons work as a group, they are given a common name using the name attribute. To group a batch of controls together, such as, in this case, the radio buttons, one can use the fieldset element. The title of such a group of controls is given by the first element in the fieldset, which has to be a legend element.

<form>
 <p><label>Customer name: <input></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
</form>

Changes from the previous step are highlighted.

To pick toppings, we can use checkboxes. These use the input element with a type attribute with the value checkbox:

<form>
 <p><label>Customer name: <input></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox> Bacon </label></p>
  <p><label> <input type=checkbox> Extra Cheese </label></p>
  <p><label> <input type=checkbox> Onion </label></p>
  <p><label> <input type=checkbox> Mushroom </label></p>
 </fieldset>
</form>

The pizzeria for which this form is being written is always making mistakes, so it needs a way to contact the customer. For this purpose, we can use form controls specifically for telephone numbers (input elements with their type attribute set to tel) and e-mail addresses (input elements with their type attribute set to email):

<form>
 <p><label>Customer name: <input></label></p>
 <p><label>Telephone: <input type=tel></label></p>
 <p><label>E-mail address: <input type=email></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox> Bacon </label></p>
  <p><label> <input type=checkbox> Extra Cheese </label></p>
  <p><label> <input type=checkbox> Onion </label></p>
  <p><label> <input type=checkbox> Mushroom </label></p>
 </fieldset>
</form>

We can use an input element with its type attribute set to time to ask for a delivery time. Many of these form controls have attributes to control exactly what values can be specified; in this case, three attributes of particular interest are min, max, and step. These set the minimum time, the maximum time, and the interval between allowed values (in seconds). This pizzeria only delivers between 11am and 9pm, and doesn't promise anything better than 15 minute increments, which we can mark up as follows:

<form>
 <p><label>Customer name: <input></label></p>
 <p><label>Telephone: <input type=tel></label></p>
 <p><label>E-mail address: <input type=email></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox> Bacon </label></p>
  <p><label> <input type=checkbox> Extra Cheese </label></p>
  <p><label> <input type=checkbox> Onion </label></p>
  <p><label> <input type=checkbox> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900"></label></p>
</form>

The textarea element can be used to provide a free-form text field. In this instance, we are going to use it to provide a space for the customer to give delivery instructions:

<form>
 <p><label>Customer name: <input></label></p>
 <p><label>Telephone: <input type=tel></label></p>
 <p><label>E-mail address: <input type=email></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox> Bacon </label></p>
  <p><label> <input type=checkbox> Extra Cheese </label></p>
  <p><label> <input type=checkbox> Onion </label></p>
  <p><label> <input type=checkbox> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900"></label></p>
 <p><label>Delivery instructions: <textarea></textarea></label></p>
</form>

Finally, to make the form submittable we use the button element:

<form>
 <p><label>Customer name: <input></label></p>
 <p><label>Telephone: <input type=tel></label></p>
 <p><label>E-mail address: <input type=email></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size> Small </label></p>
  <p><label> <input type=radio name=size> Medium </label></p>
  <p><label> <input type=radio name=size> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox> Bacon </label></p>
  <p><label> <input type=checkbox> Extra Cheese </label></p>
  <p><label> <input type=checkbox> Onion </label></p>
  <p><label> <input type=checkbox> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900"></label></p>
 <p><label>Delivery instructions: <textarea></textarea></label></p>
 <p><button>Submit order</button></p>
</form>

4.10.1.2 Implementing the server-side processing for a form

This section is non-normative.

The exact details for writing a server-side processor are out of scope for this specification. For the purposes of this introduction, we will assume that the script at https://pizza.example.com/order.cgi is configured to accept submissions using the application/x-www-form-urlencoded format, expecting the following parameters sent in an HTTP POST body:

custname: Customer's name
custtel: Customer's telephone number
custemail: Customer's e-mail address
size: The pizza size, either small, medium, or large
toppings: The topping, specified once for each selected topping, with the allowed values being bacon, cheese, onion, and mushroom
delivery: The requested delivery time
comments: The delivery instructions

4.10.1.3 Configuring a form to communicate with a server

This section is non-normative.

Form submissions are exposed to servers in a variety of ways, most commonly as HTTP GET or POST requests. To specify the exact method used, the method attribute is specified on the form element. This doesn't specify how the form data is encoded, though; to specify that, you use the enctype attribute. You also have to specify the URL of the service that will handle the submitted data, using the action attribute.

For each form control you want submitted, you then have to give a name that will be used to refer to the data in the submission. We already specified the name for the group of radio buttons; the same attribute (name) also specifies the submission name. Radio buttons can be distinguished from each other in the submission by giving them different values, using the value attribute.

Multiple controls can have the same name; for example, here we give all the checkboxes the same name, and the server distinguishes which checkbox was checked by seeing which values are submitted with that name — like the radio buttons, they are also given unique values with the value attribute.

Given the settings in the previous section, this all becomes:

<form method="post"
      enctype="application/x-www-form-urlencoded"
      action="https://pizza.example.com/order.cgi">
 <p><label>Customer name: <input name="custname"></label></p>
 <p><label>Telephone: <input type=tel name="custtel"></label></p>
 <p><label>E-mail address: <input type=email name="custemail"></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size value="small"> Small </label></p>
  <p><label> <input type=radio name=size value="medium"> Medium </label></p>
  <p><label> <input type=radio name=size value="large"> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox name="topping" value="bacon"> Bacon </label></p>
  <p><label> <input type=checkbox name="topping" value="cheese"> Extra Cheese </label></p>
  <p><label> <input type=checkbox name="topping" value="onion"> Onion </label></p>
  <p><label> <input type=checkbox name="topping" value="mushroom"> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900" name="delivery"></label></p>
 <p><label>Delivery instructions: <textarea name="comments"></textarea></label></p>
 <p><button>Submit order</button><p>
</form>

For example, if the customer entered "Denise Lawrence" as their name, "555-321-8642" as their telephone number, did not specify an e-mail address, asked for a medium-sized pizza, selected the Extra Cheese and Mushroom toppings, entered a delivery time of 7pm, and left the delivery instructions text field blank, the user agent would submit the following to the online Web service:

custname=Denise+Lawrence&custtel=555-321-8624&custemail=&size=medium&topping=cheese&topping=mushroom&delivery=19%3A00&comments=

4.10.1.4 Client-side form validation

This section is non-normative.

Forms can be annotated in such a way that the user agent will check the user's input before the form is submitted. The server still has to verify the input is valid (since hostile users can easily bypass the form validation), but it allows the user to avoid the wait incurred by having the server be the sole checker of the user's input.

The simplest annotation is the required attribute, which can be specified on input elements to indicate that the form is not to be submitted until a value is given. By adding this attribute to the customer name and delivery time fields, we allow the user agent to notify the user when the user submits the form without filling in those fields:

<form method="post"
      enctype="application/x-www-form-urlencoded"
      action="https://pizza.example.com/order.cgi">
 <p><label>Customer name: <input name="custname" required></label></p>
 <p><label>Telephone: <input type=tel name="custtel"></label></p>
 <p><label>E-mail address: <input type=email name="custemail"></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size value="small"> Small </label></p>
  <p><label> <input type=radio name=size value="medium"> Medium </label></p>
  <p><label> <input type=radio name=size value="large"> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox name="topping" value="bacon"> Bacon </label></p>
  <p><label> <input type=checkbox name="topping" value="cheese"> Extra Cheese </label></p>
  <p><label> <input type=checkbox name="topping" value="onion"> Onion </label></p>
  <p><label> <input type=checkbox name="topping" value="mushroom"> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900" name="delivery" required></label></p>
 <p><label>Delivery instructions: <textarea name="comments"></textarea></label></p>
 <p><button>Submit order</button><p>
</form>

It is also possible to limit the length of the input, using the maxlength attribute. By adding this to the textarea element, we can limit users to 1000 characters, preventing them from writing huge essays to the busy delivery drivers instead of staying focused and to the point:

<form method="post"
      enctype="application/x-www-form-urlencoded"
      action="https://pizza.example.com/order.cgi">
 <p><label>Customer name: <input name="custname" required></label></p>
 <p><label>Telephone: <input type=tel name="custtel"></label></p>
 <p><label>E-mail address: <input type=email name="custemail"></label></p>
 <fieldset>
  <legend> Pizza Size </legend>
  <p><label> <input type=radio name=size value="small"> Small </label></p>
  <p><label> <input type=radio name=size value="medium"> Medium </label></p>
  <p><label> <input type=radio name=size value="large"> Large </label></p>
 </fieldset>
 <fieldset>
  <legend> Pizza Toppings </legend>
  <p><label> <input type=checkbox name="topping" value="bacon"> Bacon </label></p>
  <p><label> <input type=checkbox name="topping" value="cheese"> Extra Cheese </label></p>
  <p><label> <input type=checkbox name="topping" value="onion"> Onion </label></p>
  <p><label> <input type=checkbox name="topping" value="mushroom"> Mushroom </label></p>
 </fieldset>
 <p><label>Preferred delivery time: <input type=time min="11:00" max="21:00" step="900" name="delivery" required></label></p>
 <p><label>Delivery instructions: <textarea name="comments" maxlength=1000></textarea></label></p>
 <p><button>Submit order</button><p>
</form>

4.10.2 Categories

Mostly for historical reasons, elements in this section fall into several overlapping (but subtly different) categories in addition to the usual ones like flow content, phrasing content, and interactive content.

A number of the elements are form-associated elements, which means they can have a form owner and, to expose this, have a form content attribute with a matching form IDL attribute.

The form-associated elements fall into several subcategories:

Listed elements

Denotes elements that are listed in the form.elements and fieldset.elements APIs.

Labelable elements

Denotes elements that can be associated with label elements.

Submittable elements

Denotes elements that can be used for constructing the form data set when a form element is submitted.

Resettable elements

Denotes elements that can be affected when a form element is reset.

In addition, some submittable elements can be, depending on their attributes, buttons. The prose below defines when an element is a button. Some buttons are specifically submit buttons.

The object element is also a form-associated element and can, with the use of a suitable plugin, partake in form submission.

4.10.3 The `form` element

Categories

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Flow content, but with no form element descendants.

Content attributes:

accept-charset

action

autocomplete

enctype

method

name

novalidate

target

DOM interface:

[OverrideBuiltins]
interface HTMLFormElement : HTMLElement {
           attribute DOMString acceptCharset;
           attribute DOMString action;
           attribute DOMString autocomplete;
           attribute DOMString enctype;
           attribute DOMString encoding;
           attribute DOMString method;
           attribute DOMString name;
           attribute boolean noValidate;
           attribute DOMString target;

  readonly attribute HTMLFormControlsCollection elements;
  readonly attribute long length;
  caller getter any (in unsigned long index);
  caller getter any (in DOMString name);

  void submit();
  void reset();
  boolean checkValidity();
};

The form element represents a collection of form-associated elements, some of which can represent editable values that can be submitted to a server for processing.

The accept-charset attribute gives the character encodings that are to be used for the submission. If specified, the value must be an ordered set of unique space-separated tokens that are ASCII case-insensitive, and each token must be an ASCII case-insensitive match for the preferred MIME name of an ASCII-compatible character encoding. [IANACHARSET]

The name attribute represents the form's name within the forms collection. The value must not be the empty string, and the value must be unique amongst the form elements in the forms collection that it is in, if any.

The autocomplete attribute is an enumerated attribute. The attribute has two states. The on keyword maps to the on state, and the off keyword maps to the off state. The attribute may also be omitted. The missing value default is the on state. The off state indicates that by default, input elements in the form will have their resulting autocompletion state set to off; the on state indicates that by default, input elements in the form will have their resulting autocompletion state set to on.

The action, enctype, method, novalidate, and target attributes are attributes for form submission.

form . elements

Returns an HTMLCollection of the form controls in the form (excluding image buttons for historical reasons).

form . length

Returns the number of form controls in the form (excluding image buttons for historical reasons).

form[index]

form(index)

Returns the indexth element in the form (excluding image buttons for historical reasons).

form[name]

form(name)

Returns the form control in the form with the given ID or name (excluding image buttons for historical reasons).

Once an element has been referenced using a particular name, that name will continue being available as a way to reference that element in this method, even if the element's actual ID or name changes, for as long as the element remains in the Document.

If there are multiple matching items, then a NodeList object containing all those elements is returned.

Returns null if no element with that ID or name could be found.

form . submit()

Submits the form.

form . reset()

Resets the form.

form . checkValidity()

Returns true if the form's controls are all valid; otherwise, returns false.

The autocomplete IDL attribute must reflect the content attribute of the same name, limited to only known values.

The name IDL attribute must reflect the content attribute of the same name.

The acceptCharset IDL attribute must reflect the accept-charset content attribute.

The elements IDL attribute must return an HTMLFormControlsCollection rooted at the Document node, whose filter matches listed elements whose form owner is the form element, with the exception of input elements whose type attribute is in the Image Button state, which must, for historical reasons, be excluded from this particular collection.

The length IDL attribute must return the number of nodes represented by the elements collection.

The supported property indices at any instant are the indices supported by the object returned by the elements attribute at that instant.

When a form element is indexed for indexed property retrieval, the user agent must return the value returned by the item method on the elements collection, when invoked with the given index as its argument.

Each form element has a mapping of names to elements called the past names map. It is used to persist names of controls even when they change names.

The supported property names are the union of the names currently supported by the object returned by the elements attribute, and the names currently in the past names map.

When a form element is indexed for named property retrieval, the user agent must run the following steps:

If name is one of the supported property names of the object returned by the elements attribute, then run these substeps:
1. Let candidate be the object returned by the namedItem() method on the object returned by the elements attribute when passed the name argument.
2. If candidate is an element, then add a mapping from name to candidate in the form element's past names map, replacing the previous entry with the same name, if any.
3. Return candidate and abort these steps.
Otherwise, name is the name of one of the entries in the form element's past names map: return the object associated with name in that map.

If an element listed in the form element's past names map is removed from the Document, then its entries must be removed from the map.

The submit() method, when invoked, must submit the form element from the form element itself, with the scripted-submit flag set.

The reset() method, when invoked, must run the following steps:

If the form element is marked as locked for reset, then abort these steps.
Mark the form element as locked for reset.
Reset the form element.
Unmark the form element as locked for reset.

If the checkValidity() method is invoked, the user agent must statically validate the constraints of the form element, and return true if the constraint validation return a positive result, and false if it returned a negative result.

This example shows two search forms:

<form action="http://www.google.com/search" method="get">
 <label>Google: <input type="search" name="q"></label> <input type="submit" value="Search...">
</form>
<form action="http://www.bing.com/search" method="get">
 <label>Bing: <input type="search" name="q"></label> <input type="submit" value="Search...">
</form>

4.10.4 The `fieldset` element

Categories

Listed form-associated element.

Contexts in which this element can be used:

Where flow content is expected.

Content model:

Optionally a legend element, followed by flow content.

Content attributes:

disabled

form

name

DOM interface:

interface HTMLFieldSetElement : HTMLElement {
           attribute boolean disabled;
  readonly attribute HTMLFormElement form;
           attribute DOMString name;

  readonly attribute DOMString type;

  readonly attribute HTMLFormControlsCollection elements;

  readonly attribute boolean willValidate;
  readonly attribute ValidityState validity;
  readonly attribute DOMString validationMessage;
  boolean checkValidity();
  void setCustomValidity(in DOMString error);
};

The fieldset element represents a set of form controls optionally grouped under a common name.

The name of the group is given by the first legend element that is a child of the fieldset element, if any. The remainder of the descendants form the group.

The disabled attribute, when specified, causes all the form control descendants of the fieldset element, excluding those that are descendants of the fieldset element's first legend element child, if any, to be disabled.

The form attribute is used to explicitly associate the fieldset element with its form owner. The name attribute represents the element's name.

fieldset . type: Returns the string "fieldset".
fieldset . elements: Returns an HTMLFormControlsCollection of the form controls in the element.

The disabled IDL attribute must reflect the content attribute of the same name.

The type IDL attribute must return the string "fieldset".

The elements IDL attribute must return an HTMLFormControlsCollection rooted at the fieldset element, whose filter matches listed elements.

Constraint validation: fieldset elements are always barred from constraint validation.

The following snippet shows a fieldset with a checkbox in the legend that controls whether or not the fieldset is enabled. The contents of the fieldset consist of two required text fields and an optional year/month control.

<fieldset name="clubfields" disabled>
 <legend> <label>
  <input type=checkbox name=club onchange="form.clubfields.disabled = !checked">
  Use Club Card
 </label> </legend>
 <p><label>Name on card: <input name=clubname required></label></p>
 <p><label>Card number: <input name=clubnum required pattern="[-0-9]+"></label></p>
 <p><label>Expiry date: <input name=clubexp type=month></label></p>
</fieldset>

You can also nest fieldset elements. Here is an example expanding on the previous one that does so:

<fieldset name="clubfields" disabled>
 <legend> <label>
  <input type=checkbox name=club onchange="form.clubfields.disabled = !checked">
  Use Club Card
 </label> </legend>
 <p><label>Name on card: <input name=clubname required></label></p>
 <fieldset name="numfields">
  <legend> <label>
   <input type=radio checked name=clubtype onchange="form.numfields.disabled = !checked">
   My card has numbers on it
  </label> </legend>
  <p><label>Card number: <input name=clubnum required pattern="[-0-9]+"></label></p>
 </fieldset>
 <fieldset name="letfields" disabled>
  <legend> <label>
   <input type=radio name=clubtype onchange="form.letfields.disabled = !checked">
   My card has letters on it
  </label> </legend>
  <p><label>Card code: <input name=clublet required pattern="[A-Za-z]+"></label></p>
 </fieldset>
</fieldset>

In this example, if the outer "Use Club Card" checkbox is not checked, everything inside the outer fieldset, including the two radio buttons in the legends of the two nested fieldsets, will be disabled. However, if the checkbox is checked, then the radio buttons will both be enabled and will let you select which of the two inner fieldsets is to be enabled.

4.10.5 The `legend` element

Categories

None.

Contexts in which this element can be used:

As the first child of a fieldset element.

Content model:

Content attributes:

DOM interface:

interface HTMLLegendElement : HTMLElement {
  readonly attribute HTMLFormElement form;
};

The legend element represents a caption for the rest of the contents of the legend element's parent fieldset element, if any.

legend . form: Returns the element's form element, if any, or null otherwise.

The form IDL attribute's behavior depends on whether the legend element is in a fieldset element or not. If the legend has a fieldset element as its parent, then the form IDL attribute must return the same value as the form IDL attribute on that fieldset element. Otherwise, it must return null.

4.10.6 The `label` element

Categories

Interactive content.

Form-associated element.

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Phrasing content, but with no descendant labelable form-associated elements unless it is the element's labeled control, and no descendant label elements.

Content attributes:

form

for

DOM interface:

interface HTMLLabelElement : HTMLElement {
  readonly attribute HTMLFormElement form;
           attribute DOMString htmlFor;
  readonly attribute HTMLElement control;
};

The label represents a caption in a user interface. The caption can be associated with a specific form control, known as the label element's labeled control, either using for attribute, or by putting the form control inside the label element itself.

Except where otherwise specified by the following rules, a label element has no labeled control.

The for attribute may be specified to indicate a form control with which the caption is to be associated. If the attribute is specified, the attribute's value must be the ID of a labelable form-associated element in the same Document as the label element. If the attribute is specified and there is an element in the Document whose ID is equal to the value of the for attribute, and the first such element is a labelable form-associated element, then that element is the label element's labeled control.

If the for attribute is not specified, but the label element has a labelable form-associated element descendant, then the first such descendant in tree order is the label element's labeled control.

The label element's exact default presentation and behavior, in particular what its activation behavior might be, if anything, should match the platform's label behavior.

For example, on platforms where clicking a checkbox label checks the checkbox, clicking the label in the following snippet could trigger the user agent to run synthetic click activation steps on the input element, as if the element itself had been triggered by the user:

<label><input type=checkbox name=lost> Lost</label>

On other platforms, the behavior might be just to focus the control, or do nothing.

label . control: Returns the form control that is associated with this element.

The form attribute is used to explicitly associate the label element with its form owner.

The htmlFor IDL attribute must reflect the for content attribute.

The control IDL attribute must return the label element's labeled control, if any, or null if there isn't one.

control . labels: Returns a NodeList of all the label elements that the form control is associated with.

Labelable form-associated elements have a NodeList object associated with them that represents the list of label elements, in tree order, whose labeled control is the element in question. The labels IDL attribute of labelable form-associated elements, on getting, must return that NodeList object.

The form IDL attribute is part of the element's forms API.

The following example shows three form controls each with a label, two of which have small text showing the right format for users to use.

<p><label>Full name: <input name=fn> <small>Format: First Last</small></label></p>
<p><label>Age: <input name=age type=number min=0></label></p>
<p><label>Post code: <input name=pc> <small>Format: AB12 3CD</small></label></p>

4.10.7 The `input` element

Categories

If the type attribute is not in the Hidden state: Interactive content.

If the type attribute is not in the Hidden state: Listed, labelable, submittable, and resettable form-associated element.

If the type attribute is in the Hidden state: Listed, submittable, and resettable form-associated element.

Contexts in which this element can be used:

Where phrasing content is expected.

Content model:

Empty.

Content attributes: