<li>An element used as an additional markup "hook" for <abbr title="Cascading Style Sheets">CSS</abbr>; or</li>

<li>A layout table and/or any of its associated rows, cells, etc.</li>

</ul>

<p>For example, the following two markup snippets will be exposed similarly to an accessibility <abbr title="Application Programing Interface">API</abbr>.</p>

<pre class="example highlight"><span class="comment">&lt;!-- 1. role="presentation" negates the implicit 'heading' role semantics but does not affect the contents, including the nested hyperlink. --&gt;</span>

&lt;h1 role="presentation"&gt; Sample Content &lt;a href="...">let's go!&lt;/a> &lt;/h1&gt;

<div class="property" id="aria-relevant">

<pdef>aria-relevant</pdef>

<div class="property-description">

<p>The <a>attribute</a> is represented as a space-separated list of the following <span>values</span>: <code>additions</code>, <code>removals</code>, <code>text</code>; or a single catch-all value <code>all</code>.</p>

<p>This is used to describe <a>semantically</a> meaningful changes, as opposed to merely presentational ones. For example, nodes that are removed from the top of a log are merely removed for purposes of creating room for other entries, and the removal of them does not have meaning. However, in the case of a buddy list, removal of a buddy name indicates that they are no longer online, and this is a meaningful <a>event</a>. In that case <pref>aria-relevant</pref> will be set to <code>all</code>. When the <pref>aria-relevant</pref> attribute is not provided, the default value, <code>additions text</code>, indicates that text modifications and node additions are relevant, but that node removals are irrelevant.</p>

<p class="note"><pref>aria-relevant</pref> values of removals or all are to be used sparingly. Assistive technologies only need to be informed of content removal when its removal represents an important change, such as a buddy leaving a chat room.</p>

<tbody>

<tr>

<th class="value-name" scope="row">additions</th>

</tr>

<tr>

<th class="value-name" scope="row"><strong class="default">additions text (default)</strong></th>

</tr>

<tr>

<th class="value-name" scope="row">removals</th>

</tr>

<tr>

<th class="value-name" scope="row">text</th>

</tr>

</tbody>

</table>

</section>

</section>

<section class="normative" id="accessibility_tree">

<p>The <a class="termref">accessibility tree</a> and the DOM tree are parallel structures. The <a class="termref">accessibility tree</a> includes the user interface objects of the <a>user agent</a> and the objects of the document. <a>Accessible objects</a> are created in the accessibility tree for every DOM element that should be exposed to an <a>assistive technology</a>, either because it may fire an accessibility <a>event</a> or because it has a [=ARIA/property=], <a>relationship</a> or feature which needs to be exposed.</p>

<section id="tree_exclusion">

<h2>Excluding Elements from the Accessibility Tree</h2>