4.4 Sections

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.

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.

4.4.2 The section element

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.

4.4.3 The nav element

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.

4.4.4 The article element

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

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.

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

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.

4.4.7 The hgroup element

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).

4.4.8 The header element

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.

4.4.9 The footer element

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.

4.4.10 The address element

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.

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.

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.

4.4.11 Headings and sections

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.

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.

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 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;
    }
  }
}

HTML5

4.4.1 The `body` element

4.4.2 The `section` element

4.4.3 The `nav` element

4.4.4 The `article` element

4.4.5 The `aside` element

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

4.4.7 The `hgroup` element

4.4.8 The `header` element

4.4.9 The `footer` element

4.4.10 The `address` element

4.4.11 Headings and sections

4.4.11.1 Creating an outline

HTML5

4.4 Sections

4.4.1 The body element

4.4.2 The section element

4.4.3 The nav element

4.4.4 The article element

4.4.5 The aside element

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

4.4.7 The hgroup element

4.4.8 The header element

4.4.9 The footer element

4.4.10 The address element

4.4.11 Headings and sections

4.4.11.1 Creating an outline

4.4.1 The `body` element

4.4.2 The `section` element

4.4.3 The `nav` element

4.4.4 The `article` element

4.4.5 The `aside` element

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

4.4.7 The `hgroup` element

4.4.8 The `header` element

4.4.9 The `footer` element

4.4.10 The `address` element