Revision 980585 of id

<div>{{HTMLSidebar("Global_attributes")}}</div>

<p>The <strong>id</strong> <a href="/en-US/docs/Web/HTML/Global_attributes">global attribute</a> defines a unique identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with CSS).</p>

<p>This attribute's value is an opaque string: this means that web author must not use it to convey any information. Particular meaning, for example semantic meaning, must not be derived from the string.</p>

<p>This attribute's value must not contain white spaces. Browsers treat non-conforming IDs that contains white spaces as if the white space is part of the ID. In contrast to the <strong>class</strong> attribute, which allows space-separated values, elements can only have one single ID defined through the <strong>id</strong> attribute. Note that an element may have several IDs, but the others should be set by another means, such as via a script interfacing with the DOM interface of the element.</p>

<div class="note">
<p><strong>Note:</strong> Using characters except ASCII letters and digits, <code>'_'</code>, <code>'-'</code> and <code>'.'</code> may cause compatibility problems, as they weren't allowed in HTML 4. Though this restriction has been lifted in HTML 5, an ID should start with a letter for compatibility.</p>
</div>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('HTML WHATWG', "dom.html#the-id-attribute", "id")}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td>No change from latest snapshot, {{SpecName('HTML5.1')}}</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5.1', "dom.html#the-id-attribute", "id")}}</td>
   <td>{{Spec2('HTML5.1')}}</td>
   <td>Snapshot of {{SpecName('HTML WHATWG')}}, no change from {{SpecName('HTML5 W3C')}}</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5 W3C', "dom.html#the-id-attribute", "id")}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>Snapshot of {{SpecName('HTML WHATWG')}}, now accept <code>'_'</code>, <code>'-'</code> and <code>'.'</code> if not at the beginning fo the id. It is also a true global attribute.</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML4.01', 'struct/global.html#adef-id', 'id')}}</td>
   <td>{{Spec2('HTML4.01')}}</td>
   <td>Supported on all elements but {{HTMLElement("base")}}, {{HTMLElement("head")}}, {{HTMLElement("html")}}, {{HTMLElement("meta")}}, {{HTMLElement("script")}}, {{HTMLElement("style")}}, and {{HTMLElement("title")}}.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<p>{{CompatibilityTable}}</p>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}<sup>[1]</sup></td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}<sup>[1]</sup></td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] <code>id</code> is a true global attribute only since Gecko 32.0 {{geckoRelease("32.0")}}.</p>

<h2 id="See_also">See also</h2>

<ul>
 <li>All <a href="/en-US/docs/Web/HTML/Global_attributes">global attributes</a>.</li>
 <li>{{domxref("Element.id")}} that reflects this attribute.</li>
</ul>