HTML 5: The Markup Language

2.01. Terms used in other parts of the specification # T

The following is a list of terms that are common to various other sections in this specification.

browsing context

A browsing context is a collection of one or more documents and one or more views.

case-insensitive match

For the purposes of this specification, performing a case-insensitive match between two strings means comparing the strings exactly, codepoint for codepoint, except that the characters in the range A-Z and the corresponding characters in the range a-z are considered to also match.

fallback content

Some embedded content elements can have fallback content: content that is to be used when the embedded content cannot be used (for example, when it is of an unsupported format).

HTML producers

HTML authors (that is, people) and applications (such as editors and content management systems) that produce HTML content.

HTML consumers

HTML user agents; that is, applications (such as Web browsers) which consume HTML content

newline

A newline may be represented as any of the following:

• a U+000D CARRIAGE RETURN (CR) character
• a U+000A LINE FEED (LF) character
• a U+000D CARRIAGE RETURN (CR) followed by a U+000A LINE FEED (LF) character

space

A space character is any of the following:

• U+0020 SPACE
• U+0009 CHARACTER TABULATION (tab)
• U+000A LINE FEED (LF)
• U+000C FORM FEED (FF)
• U+000D CARRIAGE RETURN (CR)

view

A view is as defined in Document Object Model (DOM) Level 2 Views [DOM2VIEWS].

2.02. Symbols used in content models # T

This section provides explanations for the symbols used in the Content model and Attribute model subsections of the per-element documentation in the HTML elements section and in the Common content models, Common attributes, and Forms attributes sections.

The explanations use the term group to mean any combination of names and symbols that are delimited by a pair of matching "(" and ")" (parentheses) symbols, and the term pattern name to mean any hyperlinked name used in a definition that is not an element name or an attribute name.

? (optional)

The "?" (question mark) symbol after an element name, attribute name, pattern name, or group indicates that it is optional — meaning that it can either not occur at all, or it can occur exactly once.

* (zero or more)

The "*" (asterisk) symbol after an element name, pattern name, or group indicates that it may occur any number of times, including not occurring at all.

+ (one or more)

The "+" (plus sign) symbol after an element name, pattern name, or group indicates that is must occur at least once, and can occur more than once.

| (either/or choice)

The "|" (vertical line) symbol between element names, attribute names, pattern names, and groups indicates an either/or alternative relationship between the two items it separates; that is, it indicates that either the item before the "|" symbol can occur, or the item after the symbol can occur.

, (in the order shown)

The "," (comma) symbol between element names, pattern names, and groups indicates that the two items it separates can only occur in the order shown.

& (interleaved in any order)

The "&" (ampersand) symbol between element names, attribute names, pattern names, and groups indicates that the two items it separates can occur in any order.

3.01. The HTML language and HTML and XML syntaxes # T

The term document is used in this specification to mean an instance of the HTML language.

The HTML language is the language described in this specification; it is an abstract language that applications can potentially represent in memory in any number of possible ways, and that can be transmitted using any number of possible concrete syntaxes.

This specification makes reference to two particular concrete syntaxes for the HTML language: One syntax which is referred to throughout this specification as the HTML syntax, and another syntax, which is referred to throughout this specification as the XML syntax. Web browsers typically implement two separate parsers for processing documents: an HTML parser which is invoked when processing documents in the HTML syntax, and an XML parser which is invoked when processing documents in the XML syntax.

The HTML syntax is the syntax described in the HTML syntax section of this specification.

The XML syntax is defined by rules in the XML specification [XML] and in the Namespaces in XML 1.0 specification [XMLNS]. Beyond the requirements defined in those specifications, this specification does not define any additional syntax-level requirements for documents in the XML syntax.

3.02. The HTML namespace and MIME types # T

The HTML namespace is defined as http://www.w3.org/1999/xhtml. The HTML namespace is the namespace both for documents in the HTML syntax and for documents in the XML syntax.

Documents that are served with the text/html MIME type must conform to the rules in this specification for documents in the HTML syntax.

Documents that have an HTML namespace declaration and that are served with an XML MIME type such as text/xml, application/xml, or application/xhtml+xml must conform to the rules in this specification for documents in the XML syntax.

3.03. Conformant documents # T

A conformant document in the HTML syntax must consist of the following parts, in the following order:

1. Optionally, a single U+FEFF BYTE ORDER MARK (BOM) character.
2. Any number of comments and space characters.
3. A doctype.
4. Any number of comments and space characters.
5. An html element, with its attributes and contents.
6. Any number of comments and space characters.

Documents in the HTML syntax must conform to the syntax described in the HTML syntax section of this specification.

A conformant document in the XML syntax must consist of the following parts, in the following order:

1. Optionally, a single U+FEFF BYTE ORDER MARK (BOM) character.
2. Any number of comments and space characters, as defined in the XML specification [XML].
3. Optionally, a doctype declaration, as defined in the XML specification [XML].
4. Any number of comments and space characters, as defined in the XML specification [XML].
5. An html element, with its attributes and contents.
6. Any number of comments and space characters, as defined in the XML specification [XML].

Documents in the XML syntax must conform to XML constraints as defined in the XML specification [XML] and in the Namespaces in XML 1.0 specification [XMLNS] — including XML well-formedness constraints — and must not make use of any features of the HTML syntax that do not follow XML well-formedness constraints (for example, documents in the XML syntax must not use unquoted attribute value syntax and must not omit tags).

3.04. Case insensitivity in tag names and attribute names # T

In documents in the HTML syntax:

• Tag names for HTML elements may be written with any mix of lowercase and uppercase letters that are a case-insensitive match for the names of the elements given in the HTML elements section of this document; that is, tag names are case-insensitive.
• Attribute names for HTML elements may be written with any mix of lowercase and uppercase letters that are an case-insensitive match for the names of the attributes given in the HTML elements section of this document; that is, attribute names are case-insensitive.

In documents in the XML syntax:

• Tag names for HTML elements must exactly match the names of the elements given in the HTML elements section of this document; that is, tag names are case-sensitive.
• Attribute names for HTML elements must exactly match the names of the attributes given in the HTML elements section of this document; that is, attribute names are case-sensitive.

4.01. The doctype # T

A doctype (sometimes capitalized as “DOCTYPE”) is an special instruction which, for legacy reasons that have to do with processing modes in browsers, is a required part of any document in the HTML syntax; it must either be a deprecated doctype, or must consist of the following parts, in exactly the following order:

1. A "<" character.
2. A "!" character.
3. Any case-insensitive match for the string "DOCTYPE".
4. One or more space characters.
5. Any case-insensitive match for the string "HTML".
6. Optionally, a doctype legacy string.
7. Optionally, one or more space characters.
8. A ">" character.

A doctype legacy string consists of the following parts, in exactly the following order.

1. One or more space characters.
2. Any case-insensitive match for the string "SYSTEM".
3. One or more space characters
4. A quote mark, consisting of either a """ character or a "'" character.
5. The literal string "about:legacy-compat".
6. A matching quote mark, identical to the quote mark used earlier (either a """ character or a "'" character).

<!DOCTYPE html>

<!doctype HTML system "about:legacy-compat">

A deprecated doctype is a document type declaration as defined in the XML specification [XML], with the further restriction that it must meet one of the following sets of constraints:

• The document type declaration’s name part is a case-insensitive match for the string "HTML", its public identifier is an exact match for the literal string "-//W3C//DTD HTML 4.0//EN", and its system identifier is either missing or is an exact match for the literal string "http://www.w3.org/TR/REC-html40/strict.dtd".
• The document type declaration’s name part is a case-insensitive match for the string "HTML", its public identifier is an exact match for the literal string "-//W3C//DTD HTML 4.01//EN", and its system identifier is either missing or is an exact match for the literal string "http://www.w3.org/TR/html4/strict.dtd".
• The document type declaration’s name part is a case-insensitive match for the string "HTML", its public identifier is an exact match for the literal string "-//W3C//DTD XHTML 1.0 Strict//EN", and its system identifier is either missing or is an exact match for the literal string "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd".
• The document type declaration’s name part is a case-insensitive match for the string "HTML", its public identifier is an exact match for the literal string "-//W3C//DTD XHTML 1.1//EN", and its system identifier is either missing or is an exact match for the literal string "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd".

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
  "http://www.w3.org/TR/html4/strict.dtd">

4.02. Character encoding declaration # T

A character encoding declaration is a mechanism for specifying the character encoding used to store or transmit a document.

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 the preferred 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 512 bytes of the document.

If the document does not start with a U+FEFF BYTE ORDER MARK (BOM) character, and if its encoding is not explicitly given by a Content-Type HTTP header, 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 in the encoding declaration state.

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

An ASCII-compatible character encoding is one that is a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the set 0x09, 0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A.

Documents must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

In a document the XML syntax, the XML declaration, as defined in the XML specification [XML] should be used to provide character-encoding information, if necessary.

4.03. Elements # T

An element’s content model defines the element’s structure: What contents (if any) the element can contain, as well as what attributes (if any) the element can have. The HTML elements section of this specification defines the content models for all of elements that are part of the HTML language. An element must not contain contents or attributes that are not part of its content model.

The contents of an element are any elements, character data, and comments that it contains. Attributes and their values are not considered to be the “contents” of an element.

A void element is an element whose content model does not allow it to have contents. Void elements can have attributes.

The following is a complete list of the void elements in HTML:

• area, base, br, col, command, embed, hr, img, input, link, meta, param, source

The following list describes syntax rules for the the HTML syntax. Rules for the the XML syntax are defined in the XML specification [XML].

• Tags are used to delimit the start and end of elements in markup. Elements have a start tag to indicate where they begin. Non-void elements have an end tag to indicate where they end.
• Tag names are used within element start tags and end tags to give the element’s name. HTML elements all have names that only use characters in the range 0–9, a–z, and A–Z.
• Start tags consist of the following parts, in exactly the following order:
  1. A "<" character.
  2. The element’s tag name.
  3. Optionally, one or more attributes, each of which must be preceded by one or more space characters.
  4. Optionally, one or more space characters.
  5. Optionally, a "/" character, which may be present only if the element is a void element.
  6. A ">" character.
• End tags consist of the following parts, in exactly the following order:
  1. A "<" character.
  2. A "/" character
  3. The element’s tag name.
  4. Optionally, one or more space characters.
  5. A ">" character.
• Void elements only have a start tag; end tags must not be specified for void elements.
• The start and end tags of certain elements can be omitted. The subsection for each element in the HTML elements section of this specification provides information about which tags (if any) can be omitted for that particular element.
• A non-void element must have an end tag, unless the subsection for that element in the HTML elements section of this specification indicates that its end tag can be omitted.
• The contents of an element must be placed between just after its start tag (which might be implied, in certain cases) and just before its end tag (which might be implied in certain cases).

<b>foo <i>bar</b> baz</i>

4.04. Attributes # T

Attributes for an element are expressed inside the element’s start tag. Attributes have a name and a value.

There must never be two or more attributes on the same start tag whose names are a case-insensitive match for each other.

The following list describes syntax rules for attributes in documents in the HTML syntax. Syntax rules for attributes in documents in the XML syntax. are defined in the XML specification [XML].

• Attribute names must consist of one or more characters other than the space characters, U+0000 NULL, """, "'", ">", "/", "=", the control characters, and any characters that are not defined by Unicode.
• XML-compatible attribute names are those that match the Name production defined in the XML specification [XML] and that contain no ":" characters, and whose first three characters are not a case-insensitive match for the string "xml".
• Attribute values, in general, are normal character data; however, the HTML elements section of this specification defines further restrictions on the allowed values of all attributes that are part of the HTML language. An attribute must not have a value that is not allowed by the content model of the element that contains it.

In the the HTML syntax, attributes can be specified in four different ways:

1. empty attribute syntax
2. unquoted attribute-value syntax
3. single-quoted attribute-value syntax
4. double-quoted attribute-value syntax

Empty attribute syntax

Certain attributes may be specified by providing just the attribute name.

In the following example, the disabled attribute is given with the empty attribute syntax:

<input disabled>

Unquoted attribute-value syntax

An unquoted attribute value is specified by providing the following parts in exactly the following order:

1. an attribute name
2. zero or more space characters
3. a single "=" character
4. zero or more space characters
5. an attribute value

In addition to the general requirements given above for attribute values, an unquoted attribute value has the following restrictions:

• must not contain any literal space characters
• must not contain any """, "'", ">", "=", characters
• must not be the empty string

In the following example, the value attribute is given with the unquoted attribute value syntax:

<input value=yes>

If the value of an attribute using the unquoted attribute syntax is followed by a "/" character, then there must be at least one space character after the value and before the "/" character.

Single-quoted attribute-value syntax

A single-quoted attribute value is specified by providing the following parts in exactly the following order:

1. an attribute name
2. zero or more space characters
3. a "=" character
4. zero or more space characters
5. a single "'" character
6. an attribute value
7. a "'" character.

In addition to the general requirements given above for attribute values, a single-quoted attribute value has the following restriction:

• must not contain any literal "'" characters

In the following example, the type attribute is given with the single-quoted attribute value syntax:

<input type='checkbox'>

Double-quoted attribute-value syntax

A double-quoted attribute value is specified by providing the following parts in exactly the following order:

1. an attribute name
2. zero or more space characters
3. a single "=" character
4. zero or more space characters
5. a single """ character
6. an attribute value
7. a """ character

In addition to the general requirements given above for attribute values, a double-quoted attribute value has the following restriction:

• must not contain any literal """ characters

In the following example, the title attribute is given with the double-quoted attribute value syntax:

<code title="U+003C LESS-THAN SIGN">&lt;</code>

4.05. Text and character data # T

Text in element contents (including in comments) and attribute values must consist of Unicode characters, with the following restrictions:

• must not contain U+0000 characters
• must not contain permanently undefined Unicode characters
• must not contain control characters other than space characters

There are two special types of text, known as escaping text span starts and escaping text span ends, that can occur within certain elements.

Character data contains text, in some cases in combination with character references, along with certain additional restrictions. There are three types of character data that can occur in documents:

1. normal character data
2. replaceable character data
3. non-replaceable character data

Normal character data

Certain elements and strings in the values of particular attributes contain normal character data. Normal character data can contain the following:

• text
• character references

Normal character data has the following restrictions:

• must not contain any "<" characters
• must not contain any ambiguous ampersands
• must not contain any escaping text spans

Replaceable character data

In documents in the HTML syntax, the title and textarea elements can contain replaceable character data. Replaceable character data can contain the following:

• text, optionally including "<" characters and escaping text spans
• character references

Replaceable character data has the following restrictions:

• must not contain any ambiguous ampersands
• must not contain any occurrences of the string "</" followed by characters that are a case-insensitive match for the tag name of the element containing the replaceable character data (for example, "</title" or "</textarea"), followed by one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), U+0020 SPACE, ">", or "/", unless that string is part of an escaping text span.

Replaceable character data, as defined in this specification, is a feature of the HTML syntax that is not available in the XML syntax. Documents in the XML syntax must not contain replaceable character data as defined in this specification; instead they must conform to all syntax constraints defined in the XML specification [XML].

Non-replaceable character data

In documents in the HTML syntax, the script, and style elements can contain non-replaceable character data. Non-replaceable character data can contain the following:

• text, optionally including "<" characters and escaping text spans
• ambiguous ampersands

Non-replaceable character data has the following restrictions:

• must not contain character references
• must not contain any occurrences of the string "</", followed by characters that are a case-insensitive match for the tag name of the element containing the replaceable character data (for example, "</script" or "</style", followed by one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000C FORM FEED (FF), U+0020 SPACE, ">", or "/", unless that string is part of an escaping text span.

Non-replaceable character data, as defined in this specification, is a feature of the HTML syntax that is not available in the XML syntax. Documents in the XML syntax must not contain non-replaceable character data as defined in this specification; instead they must conform to all syntax constraints defined in the XML specification [XML].

4.06. Character references # T

Character references are a form of markup for representing single individual characters. There are three types of character references:

• named character references
• decimal numeric character references
• hexadecimal numeric character references

Named character reference

Named character references consist of the following parts in exactly the following order:

1. An "&" character.
2. One of the entity names defined in XML Entity definitions for Characters [Entities], using the same case.
3. A ";" character.

The following is an example of a named character reference for the character "†" (U+2020 DAGGER).

†

Decimal numeric character reference

Decimal numerical character references consist of the following parts, in exactly the following order.

1. An "&" character.
2. A "#" character.
3. One or more digits in the range 0–9, representing a base-ten integer that itself is a Unicode code point that is not U+0000, U+000D, in the range U+0080–U+009F, or in the range 0xD8000–0xDFFF (surrogates).
4. A ";" character.

The following is an example of a decimal numeric character reference for the character "†" (U+2020 DAGGER).

†

Hexadecimal numeric character reference

Hexadecimal numeric character references consist of the following parts, in exactly the following order.

1. An "&" character.
2. A "#" character.
3. Either a "x" character or a "X" character.
4. One or more digits in the range 0–9, a–f, and A–F, representing a base-sixteen integer that itself is a Unicode code point that is not U+0000, U+000D, in the range U+0080–U+009F, or in the range 0xD800–0xDFFF (surrogates).
5. A ";" character.

The following is an example of a hexadecimal numeric character reference for the character "†" (U+2020 DAGGER).

†

Character references are not themselves text, and no part of a character reference is text.

An ambiguous ampersand is an "&" character that is followed by some text other than a space character, a "<", character, or another "&" character.

4.07. Comments # T

Comments consist of the following parts, in exactly the following order:

1. the comment start delimiter "<!--"
2. text
3. the comment end delimiter "-->"

The text part of comments has the following restrictions:

• must not start with a ">" character
• must not start with the string "->"
• must not contain the string "--"
• must not end with a "-" character

<!-- main content starts here -->

4.08. Escaping text spans # T

An escaping text span is a span of text that starts with an escaping text span start that is not itself in an escaping text span, and ends at the next escaping text span end. Escaping text spans have the following restriction:

• must not contain any character references

An escaping text span start is the text string "<!--".

An escaping text span end is the text string "-->".

An escaping text span start may share its "-" characters with its corresponding escaping text span end.

The text in style, script, title, and textarea elements must not have an escaping text span start that is not followed by an escaping text span end.

<style>
<!--
dfn { font-weight: bold; color: brown; }
-->
</style>

4.09. SVG and MathML elements in HTML documents # T

SVG and MathML elements are elements from the SVG and MathML namespaces. SVG and MathML elements can be used both in documents in the HTML syntax and in documents in the XML syntax. Syntax rules for SVG and MathML elements in documents in the XML syntax are defined in the XML specification [XML]. The following list describes additional syntax rules that specifically apply to SVG and MathML elements in documents in the HTML syntax.

• SVG and MathML elements whose start tags have a single "/" character before the closing ">" character are said to be marked as self-closing.
• SVG and MathML elements must either have a start tag and an end tag, or a start tag that is marked as self-closing, in which case they must not have an end tag.
• SVG and MathML elements whose start tag is marked as self-closing, can’t have any contents.
• The contents of an SVG or MathML element whose start tag is not marked as self-closing are any elements, character data, comments, and CDATA sections that it contains, with the restriction that any character data it contains must be normal character data.

4.10. CDATA sections in SVG and MathML contents # T

CDATA sections in SVG and MathML contents in documents in the HTML syntax consist of the following parts, in exactly the following order:

1. the CDATA start delimiter "<![CDATA["
2. text, with the additional restriction that the text must not contain the string "]]>“
3. the CDATA end delimiter "]]>"

CDATA sections are allowed only in the contents of elements from the SVG and MathML namespaces.

<annotation encoding="text/latex">
  <![CDATA[\documentclass{article}
  \begin{document}
  \title{E}
  \maketitle
  The base of the natural logarithms, approximately 2.71828.
  \end{document}]]>
</annotation>

a – hyperlink # T

abbr – abbreviation # T

address – contact information # T

area – image-map hyperlink # T

article – article # T

aside – tangential content # T

audio – audio stream # T

b – offset text typically styled in bold # T

base – base URL # T

bdo – BiDi override # T

blockquote – block quotation # T

body – document body # T

br – line break # T

button # T

button type=submit – submit button # T

button type=reset – reset button # T

button type=button – button with no additional semantics # T

canvas – canvas for dynamic graphics # T

caption – table title # T

cite – cited title of a work # T

code – code fragment # T

col – table column # T

colgroup – table column group # T

command # T

command type=command – command with an associated action # T

command type=radio – selection of one item from a list of items # T

command type=checkbox – state or option that can be toggled # T

datalist – predefined options for other controls # T

dd – description/value or span of discourse/quote # T

del – deleted text # T

details – additional on-demand information # T

dfn – defining instance # T

dialog – conversation # T

div – generic flow container # T

dl – description list # T

dt – term/name or talker/speaker # T

em – emphatic stress # T

embed – integration point for plugins # T

fieldset – set of related form controls # T

figure – figure with optional caption # T

footer – footer # T

form – user-submittable form # T

h1 – heading (level 1) # T

h2 – heading (level 2) # T

h3 – heading (level 3) # T

h4 – heading (level 4) # T

h5 – heading (level 5) # T

h6 – heading (level 6) # T

head – document metadata # T

header – header # T

hgroup – heading group # T

hr – thematic break # T

html – root element # T

i – offset text typically styled in italic # T

iframe – nested browsing context (inline frame) # T

img – image # T

input # T

input type=text – text-input field # T