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  <title>Selectors API Level 2</title>

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   <h1 id=title>Selectors API Level 2</h1>
   <!-- "DOM Selectors" was not acceptable. "DOM Level 4 Selectors" and
		conforming to the DOM specification template (if there is such a thing) is
		just silly so we got stuck with this weird name. -->

   <h2 class="no-num no-toc" id=W3C-doctype>W3C Working Draft 19 January 2010</h2>

   <dl>
    <dt>This Version:

    <dd><a
     href="http://www.w3.org/TR/2010/WD-selectors-api2-20100119/">http://www.w3.org/TR/2010/WD-selectors-api2-20100119/</a>

    <dt>Latest Version:

    <dd><a
     href="http://www.w3.org/TR/selectors-api2/">http://www.w3.org/TR/selectors-api2/</a>

    <dt>Previous Versions:

    <dd>None.

    <dt>Editors:

    <dd><a href="http://lachy.id.au/">Lachlan Hunt</a> (<a
     href="http://www.opera.com/">Opera Software ASA</a>) &lt;<a
     href="mailto:lachlan.hunt@lachy.id.au">lachlan.hunt@lachy.id.au</a>&gt;
   </dl>

   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
    © 2006-2007 <a href="http://www.w3.org/"><acronym title="World Wide Web
    Consortium">W3C</acronym></a><sup>®</sup> (<a
    href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
    of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
    title="European Research Consortium for Informatics and
    Mathematics">ERCIM</acronym></a>, <a
    href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a
    href="http://www.w3.org/Consortium/Legal/copyright-documents">document
    use</a> rules apply.</p>
  </div>

  <hr>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p>Selectors, which are widely used in CSS, are patterns that match against
   elements in a tree structure <a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a><a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{CSS21}}--></a>. The Selectors API
   specification defines methods for retrieving <code><a
   href="#dom-element">Element</a></code> nodes from the <abbr
   title="Document Object Model">DOM</abbr> by matching against a group of
   selectors, and for testing if a given element matches a particular
   selector. It is often desirable to perform DOM operations on a specific
   set of elements in a document. These methods simplify the process of
   acquiring and testing specific elements, especially compared with the more
   verbose techniques defined and used in the past.

  <h2 class="no-num no-toc" id=sotd>Status of this Document</h2>

  <p><em>This section describes the status of this document at the time of
   its publication. Other documents may supersede this document. A list of
   current W3C publications and the latest revision of this technical report
   can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
   index</a> at http://www.w3.org/TR/.</em>

  <p>This is the 19 January First Public Working Draft of "Selectors API
   Level 2". The W3C Membership and other interested parties are invited to
   review the document and send comments to <a
   href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> (<a
   href="http://lists.w3.org/Archives/Public/public-webapps/">public
   archive</a>) with <kbd>[selectors-api]</kbd> in the subject.

  <p><span class=notetoeditor>The editor’s copy of this specification is <a
   href="http://dev.w3.org/2006/webapi/selectors-api/">available in W3C
   CVS</a>. A detailed list of changes is also available <a
   href="http://dev.w3.org/cvsweb/2006/webapi/selectors-api/">from the CVS
   server</a>.</span>

  <p>Implementors should be aware that this specification is not stable.
   <strong>Implementors who are not taking part in the discussions are likely
   to find the specification changing out from under them in incompatible
   ways.</strong> Vendors interested in implementing this specification
   before it eventually reaches the Candidate Recommendation stage should
   join the aforementioned mailing lists and take part in the discussions.

  <p>This document was developed by the <a
   href="http://www.w3.org/2008/webapps/">Web Applications Working Group</a>.
   The Working Group expects to advance this Working Draft to Recommendation
   Status.

  <p>Publication as a Working Draft does not imply endorsement by the W3C
   Membership. This is a draft document and may be updated, replaced or
   obsoleted by other documents at any time. It is inappropriate to cite this
   document as other than work in progress.

  <p>This document was produced by a group operating under the <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
   2004 W3C Patent Policy</a>. W3C maintains a <a
   href="http://www.w3.org/2004/01/pp-impl/42538/status"
   rel=disclosure>public list of any patent disclosures</a> made in
   connection with the deliverables of the group; that page also includes
   instructions for disclosing a patent. An individual who has actual
   knowledge of a patent which the individual believes contains <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
   6 of the W3C Patent Policy</a>.

  <h2 class="no-num no-toc" id=toc>Table of Contents</h2>
  <!--begin-toc-->

  <ul class=toc>
   <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
    <ul class=toc>
     <li><a href="#examples"><span class=secno>1.1. </span>Examples</a>
    </ul>

   <li><a href="#conformance"><span class=secno>2. </span>Conformance
    Requirements</a>
    <ul class=toc>
     <li><a href="#terminology"><span class=secno>2.1. </span>Terminology and
      Conventions</a>
    </ul>

   <li><a href="#interoperability"><span class=secno>3.
    </span>Interoperability Considerations</a>
    <ul class=toc>
     <li><a href="#extensibility"><span class=secno>3.1.
      </span>Extensibility</a>
    </ul>

   <li><a href="#security"><span class=secno>4. </span>Security
    Considerations</a>

   <li><a href="#privacy"><span class=secno>5. </span>Privacy Considerations
    </a>

   <li><a href="#the-apis"><span class=secno>6. </span>The APIs</a>
    <ul class=toc>
     <li><a href="#nodeselector"><span class=secno>6.1. </span>The <code
      title="">NodeSelector</code> Interface</a>

     <li><a href="#matchtesting"><span class=secno>6.2. </span>Matching
      Elements</a>

     <li><a href="#processing-selectors"><span class=secno>6.3.
      </span>Processing Selectors</a>

     <li><a href="#processing-reference-nodes"><span class=secno>6.4.
      </span>Processing Reference Nodes</a>

     <li><a href="#resolving-namespaces"><span class=secno>6.5.
      </span>Resolving Namespaces</a>
    </ul>

   <li><a href="#the-scope-pseudo-class"><span class=secno>7. </span>The
    <code>:scope</code> Pseudo-Class</a>

   <li><a href="#dom-feature-string"><span class=secno>8. </span>DOM Feature
    String</a>

   <li><a href="#examples0"><span class=secno>9. </span>Examples</a>

   <li class=no-num><a href="#references">References</a>
    <ul class=toc>
     <li class=no-num><a href="#normative-references">Normative
      references</a>

     <li class=no-num><a href="#informative-references">Informative
      references</a>
    </ul>

   <li class=no-num><a href="#acknowledgements">Acknowledgements</a>
  </ul>
  <!--end-toc-->

  <h2 id=introduction><span class=secno>1. </span>Introduction</h2>

  <p><em>This section is non-normative.</em>

  <p>This specification provides methods for selecting and testing elements
   based on whether or not they match a given selector. With these methods
   methods, it is easier to match a set of <code><a
   href="#dom-element">Element</a></code> nodes based on specific criteria,
   than having to subsequently filter the result of calling other methods
   like <code>getElementsByTagName()</code>.

  <h3 id=examples><span class=secno>1.1. </span>Examples</h3>

  <p><em>This section is non-normative.</em>

  <p>Some ECMAScript <a href="#ECMA-262"
   rel=biblioentry>[ECMA-262]<!--{{ECMA-262}}--></a> examples:

  <div class=example>
   <p>This is an example table written in HTML 4.01.</p>

   <pre>&lt;table id="score">
  &lt;thead>
    &lt;tr>
      &lt;th>Test
      &lt;th>Result
  &lt;tfoot>
    &lt;tr>
      &lt;th>Average
      &lt;td>82%
  &lt;tbody>
    &lt;tr>
      &lt;td>A
      &lt;td>87%
    &lt;tr>
      &lt;td>B
      &lt;td>78%
    &lt;tr>
      &lt;td>C
      &lt;td>81%
&lt;/table></pre>

   <p>In order to obtain the cells containing the results in the table, which
    might be done, for example, to plot the values on a graph, there are at
    least two approaches that may be taken. Using only the APIs from DOM
    Level 2, it requires a script like the following that iterates through
    each <code>tr</code> within each <code>tbody</code> in the
    <code>table</code> to find the second cell of each row.</p>

   <pre>var table = document.getElementById("score");
var groups = table.tBodies;
var rows = null;
var cells = [];

for (var i = 0; i &lt; groups.length; i++) {
  rows = groups[i].rows;
  for (var j = 0; j &lt; rows.length; j++) {
    cells.push(rows[j].cells[1]);
  }
}</pre>

   <p>Alternatively, using the <code
    title=document-selectallelements>querySelectorAll()</code> method, that
    script becomes much more concise.</p>

   <pre>var cells = document.querySelectorAll("#score&gt;tbody&gt;tr&gt;td:nth-of-type(2)");</pre>

   <p>Note that the script operates on the DOM and works independently from
    the syntax used to create the document. Thus this script will also work
    correctly for an equivalent table created from well-formed XHTML instead
    of HTML, or dynamically created and inserted into a document using DOM
    APIs.</p>
  </div>

  <h2 id=conformance><span class=secno>2. </span>Conformance Requirements</h2>

  <p>All diagrams, examples and notes in this specification are
   non-normative, as are all sections explicitly marked non-normative.
   Everything else in this specification is normative.

  <p>The key words <em class=ct>must</em>, <em class=ct>must not</em>, <em
   class=ct>should</em>, <em class=ct>may</em> and <em
   class=ct>recommended</em> in the normative parts of this document are to
   be interpreted as described in RFC 2119 <a href="#RFC2119"
   rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>.

  <p>The following conformance classes are defined (and considered) by this
   specification:

  <dl>
   <dt><dfn id=conforming-user-agent>conforming user agent</dfn>

   <dd>A user agent that implements the <code><a
    href="#dom-node-selector">NodeSelector</a></code> interface described in
    this specification and conforms to all <em class=ct>must</em>-level
    criteria that apply to implementations.

   <dt><dfn id=conforming-application>conforming application</dfn>

   <dd>An application that uses the interfaces defined in this specification
    and conforms to all <em class=ct>must</em>-level criteria that apply to
    applications.
  </dl>

  <h3 id=terminology><span class=secno>2.1. </span>Terminology and
   Conventions</h3>

  <p>The terminology used in this specification is that from Selectors <a
   href="#SELECT" rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>.

  <p>Conformance requirements phrased as algorithms or specific steps <em
   class=ct>may</em> be implemented in any manner, so long as the end result
   is equivalent.

  <p>The IDL used in this specification uses the syntax defined in Web IDL <a
   href="#WEBIDL" rel=biblioentry>[WEBIDL]<!--{{!WEBIDL}}--></a>.

  <p>The construction "<code>Foo</code> object", where <code>Foo</code> is
   actually an interface, is sometimes used instead of the more accurate
   "object implementing the <code>Foo</code> interface".

  <p>The interfaces used within, but not defined by, this specification,
   including <code>Document</code>, <code>DocumentFragment</code>,
   <code>Node</code> and <code><a href="#dom-element">Element</a></code> are
   defined in DOM Level 3 Core <a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a>.

  <h2 id=interoperability><span class=secno>3. </span>Interoperability
   Considerations</h2>

  <p><em>This section is non-normative.</em>

  <p>Some implementations might have different levels of support for
   Selectors. If some implementations lack support for some selectors, then
   the use of such selectors will result in those implementations failing to
   return the expected results. Authors are advised to check for the DOM
   Exceptions thrown by these APIs and provide a fallback for graceful
   degradation.

  <h3 id=extensibility><span class=secno>3.1. </span>Extensibility</h3>

  <p><em>This section is non-normative.</em>

  <p>Extensions of the APIs defined in this specification are <em>strongly
   discouraged</em>. Implementors, Working Groups and other interested
   parties should discuss extensions on a relevant public forum, such as <a
   href="mailto:public-webapps@w3.org">public-webapps@w3.org</a>.

  <h2 id=security><span class=secno>4. </span>Security Considerations</h2>

  <p>It is expected that implementing this specification introduces no new
   security risks for users.

  <p>If, at any time, the implementation detects a situation which would
   violate security policies, the implementation <em class=ct>may</em> abort
   and raise a security exception. If any other error condition occurs which
   is not covered directly by this or any other relevant specification, the
   implementation <em class=ct>may</em> abort and raise an appropriate,
   language-binding-specific or implementation-specific exception.

  <h2 id=privacy><span class=secno>5. </span>Privacy Considerations</h2>

  <p>History theft is a potential privacy issue because the
   <code>:visited</code> pseudo-class in Selectors <a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a> allows authors to query
   which links have been visited.

  <p class=note>This is not a new problem, as it can already be exploited
   using existing CSS and DOM APIs, such as <code>getComputedStyle()</code>
   <a href="#DOM-LEVEL-2-STYLE"
   rel=biblioentry>[DOM-LEVEL-2-STYLE]<!--{{DOM-LEVEL-2-STYLE}}--></a>.

  <div class=example>
   <p>In this example, <var>vlinks</var> will acquire a list of links that
    the user has visited. The author can then obtain the URIs and potentially
    exploit this knowledge.</p>

   <pre>var vlinks = document.querySelectorAll(":visited");
for (var i = 0; i &lt; vlinks.length; i++) {
  doSomethingEvil(vlinks[i].href);
}</pre>
  </div>

  <p>As <a href="http://www.w3.org/TR/css3-selectors/#link">defined in
   <cite>Selectors</cite></a> (<a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 6.6.1), user
   agents <em class=ct>may</em> treat all links as unvisited links. It is <em
   class=ct>recommended</em> that implementations behave consistently with
   other uses of Selectors supported by the user agent.

  <h2 id=the-apis><span class=secno>6. </span>The APIs</h2>

  <p>The term <dfn id=first>first</dfn> used in the definitions of the
   methods defined in this specification means <em>first in document
   order</em>. The term <dfn id=document-order>document order</dfn> means a
   depth-first pre-order traversal of the DOM tree or subtree in question.
   The term <dfn id=context-node>context node</dfn> refers to the node upon
   which the method was invoked. The term <dfn id=subtrees>subtrees</dfn>
   refers to the collection of elements that are descendants of the specified
   node. The term <dfn id=matching-element-node>matching <code>Element</code>
   node</dfn> refers to an <code><a href="#dom-element">Element</a></code>
   node that matches the group of selectors (<var>selectors</var>) that was
   passed to the method, according to the rules for matching elements defined
   in Selectors <a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>.

  <h3 id=nodeselector><span class=secno>6.1. </span>The <code
   title="">NodeSelector</code> Interface</h3>

  <pre class=idl>module dom {
  [Supplemental, NoInterfaceObject]
  interface <dfn id=dom-node-selector>NodeSelector</dfn> {
    Element   <a href="#queryselector" title=queryselector>querySelector</a>(in DOMString selectors, in optional any refNodes);
    NodeList  <a href="#queryselectorall" title=queryselectorall>querySelectorAll</a>(in DOMString selectors, in optional any refNodes);
    Element   <a href="#queryscopedselector" title=queryscopedselector>queryScopedSelector</a>(in DOMString selectors);
    NodeList  <a href="#queryscopedselectorall" title=queryscopedselectorall>queryScopedSelectorAll</a>(in DOMString selectors);
  };
  Document implements NodeSelector;
  DocumentFragment implements NodeSelector;
  Element implements NodeSelector;
};</pre>

  <p>The <var>selectors</var> argument for the <code><a
   href="#queryselector">querySelector</a></code> and <code><a
   href="#queryselectorall">querySelectorAll</a></code> method accepts a <a
   href="#selector-string">selector string</a>.

  <p>The <var>selectors</var> argument for the <code><a
   href="#queryscopedselector">queryScopedSelector</a></code> and <code><a
   href="#queryscopedselectorall">queryScopedSelectorAll</a></code> methods
   accepts a <a href="#scoped-selector-string">scoped selector string</a>.

  <p>The optional <var>refNodes</var> argument specifies one or more <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes.

  <p>When either method is invoked, the implementation must follow these
   steps.

  <p>If the <var>selectors</var> argument is a <a
   href="#selector-string">selector string</a>, let <var>parsed
   selector</var> be the result of running the algorithm to <a
   href="#parse-a-selector">parse a selector</a> with <var>selectors</var> as
   the input.

  <p>If the <var>selectors</var> argument is a <a
   href="#scoped-selector-string">scoped selector string</a>, let <var>parsed
   selector</var> be the result of running the algorithm to <a
   href="#parse-a-scoped-selector">parse a scoped selector</a> using
   <var>selectors</var> as the input.

  <p>Let <var>reference nodes</var> be the result of running the algorithm to
   <a href="#determine-contextual-reference-nodes">determine contextual
   reference nodes</a> using <var>refNodes</var> as the input, if provided.

  <p>The implementation must then run the algorithm to <a
   href="#evaluate-a-selector">evaluate a selector</a> against element nodes
   in the tree using <var>parsed selector</var> as the selector and
   <var>reference nodes</var> as the <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes, as needed to return the required result for invoked method.

  <p>The <dfn id=queryselector
   title=queryselector><code>querySelector()</code></dfn> method on the
   <code><a href="#dom-node-selector">NodeSelector</a></code> interface <em
   class=ct>must</em> return the <a href="#first">first</a> matching <code><a
   href="#dom-element">Element</a></code> node within the <a
   href="#subtrees">subtrees</a> of the <a href="#context-node">context
   node</a>. If there is no such node, the method <em class=ct>must</em>
   return <code>null</code>.

  <p>The <dfn id=queryselectorall
   title=queryselectorall><code>querySelectorAll()</code></dfn> method on the
   <code><a href="#dom-node-selector">NodeSelector</a></code> interface <em
   class=ct>must</em> return a <code>NodeList</code> containing all of the
   matching <code><a href="#dom-element">Element</a></code> nodes within the
   <a href="#subtrees">subtrees</a> of the <a href="#context-node">context
   node</a>, in <a href="#document-order">document order</a>. If there are no
   such nodes, the method <em class=ct>must</em> return an empty
   <code>NodeList</code>.

  <p>The <dfn id=queryscopedselector
   title=queryscopedselector><code>queryScopedSelector()</code></dfn> method
   on the <code><a href="#dom-node-selector">NodeSelector</a></code>
   interface <em class=ct>must</em>, when invoked, return the <a
   href="#first">first</a> matching <code><a
   href="#dom-element">Element</a></code> node within the entire DOM tree in
   which the <a href="#context-node">context node</a> is located. If there is
   no such node, the method <em class=ct>must</em> return <code>null</code>.

  <p>The <dfn id=queryscopedselectorall
   title=queryscopedselectorall><code>queryScopedSelectorAll()</code></dfn>
   method on the <code><a href="#dom-node-selector">NodeSelector</a></code>
   interface <em class=ct>must</em> return a <code>NodeList</code> containing
   all of the matching <code><a href="#dom-element">Element</a></code> nodes
   within the entire DOM tree in which the <a href="#context-node">context
   node</a> is located, in <a href="#document-order">document order</a>. If
   there are no such nodes, the method <em class=ct>must</em> return an empty
   <code>NodeList</code>.

  <p>The <code>NodeList</code> object returned by the <code><a
   href="#queryselectorall">querySelectorAll()</a></code> and <code><a
   href="#queryscopedselectorall">queryScopedSelectorAll()</a></code> methods
   <em class=ct>must</em> be static, not <a
   href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#td-live"
   title="Document Object Model Core">live</a> (<a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a>,
   section 1.1.1). Subsequent changes to the structure of the underlying
   document <em class=ct>must not</em> be reflected in the
   <code>NodeList</code> object. This means that the object will instead
   contain a list of matching <code><a href="#dom-element">Element</a></code>
   nodes that were in the document at the time the list was created.

  <h3 id=matchtesting><span class=secno>6.2. </span>Matching Elements</h3>

  <pre class=idl>module dom {
  [Supplemental]
  interface <dfn id=dom-element>Element</dfn> {
    boolean   <a href="#matchesselector" title=matchesselector>matchesSelector</a>(in DOMString selectors, in optional any refNodes]);
  };
};</pre>

  <p>The <var>selectors</var> argument accepts a <a
   href="#selector-string">selector string</a>.

  <p>The optional <var>refNodes</var> argument specifies one or more <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes.

  <p>When the method is invoked, the implementation must follow these steps.

  <p>Let <var>parsed selector</var> be the result of running the algorithm to
   <a href="#parse-a-selector">parse a selector</a> with <var>selectors</var>
   as the input.

  <p>Let <var>reference nodes</var> be the result of running the algorithm to
   <a href="#determine-contextual-reference-nodes">determine contextual
   reference nodes</a> using <var>refNodes</var> as the input, if provided.

  <p>The implementation must then run the algorithm to <a
   href="#evaluate-a-selector">evaluate a selector</a> against the <a
   href="#context-node">context node</a> using <var>parsed selector</var> as
   the selector and <var>reference nodes</var> as the <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes.

  <p>The <dfn id=matchesselector
   title=matchesselector><code>matchesSelector()</code></dfn> method on the
   <code><a href="#dom-element">Element</a></code> interface <em
   class=ct>must</em>, when invoked, return true if the <a
   href="#context-node">context node</a> is a <a
   href="#matching-element-node">matching <code>Element</code> node</a>.
   Otherwise, the method <em class=ct>must</em> return false.

  <h3 id=processing-selectors><span class=secno>6.3. </span>Processing
   Selectors</h3>

  <p>A <dfn id=selector-string>selector string</dfn> is a <a
   href="http://www.w3.org/TR/css3-selectors/#grouping">group of
   selectors</a> (<a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 5). This group of
   selectors <em class=ct>should</em> match the <code>selectors_group</code>
   production (<a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 10) with the
   additional provision that leading and trailing <a
   href="http://www.w3.org/TR/css3-selectors/#whitespace"
   title=Selectors>whitespace</a> (<a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 4) is permitted.
   This group of selectors <em class=ct>should not</em> use <a
   href="#namespace-prefix-needs-to-be-resolved"
   title=need-to-resolve>namespace prefixes that need to be resolved</a>.

  <p>A <dfn id=scoped-selector-string>scoped selector string</dfn> is a <a
   href="http://www.w3.org/TR/css3-selectors/#grouping">group of
   selectors</a> (<a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 5), that will
   imply the presence of the <code><a href="#scope">:scope</a></code>
   pseudo-class at the beginning, if not specified explicilty.

  <p class=note>Implementers are advised that if <code>null</code> or
   <code>undefined</code> are passed as the value of the <var>selectors</var>
   parameter, they are to be handled as defined in WebIDL <a href="#WEBIDL"
   rel=biblioentry>[WEBIDL]<!--{{!WEBIDL}}--></a>. Authors are advised to
   avoid passing these values.

  <p class=note>Authors are advised that while the use of pseudo-elements in
   selectors is permitted, they will not match any elements in the document,
   and thus would not result in any elements being returned. Therefore,
   authors are advised to avoid the use of pseudo-elements in selectors that
   are passed to the methods defined in this specification.

  <p>The steps to <dfn id=parse-a-selector>parse a selector</dfn> are as
   follows:

  <ol>
   <li>Let <var>input</var> be the input to this algorithm.

   <li>The implementation <em class=ct>must</em> first trim any leading
    and/or trailing <a href="http://www.w3.org/TR/css3-selectors/#whitespace"
    title=Selectors>whitespace</a> from <var>input</var>.

   <li>Let <var>result</var> be the group of selectors returned as a result
    of parsing the <var>input</var> according to <a
    href="http://www.w3.org/TR/css3-selectors/#w3cselgrammar">the grammar of
    Selectors</a> (<a href="#SELECT"
    rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section 10).

   <li>Return <var>result</var>.
  </ol>

  <p>The steps for <dfn id=parse-a-scoped-selector>parse a scoped
   selector</dfn> are as follows:

  <ol>
   <li>Let <var>input</var> be the string being parsed.

   <li>Let <var>result</var> be the result of running the algorithm to <a
    href="#parse-a-selector">parse a selector</a> with <var>input</var> as
    the input.

   <li>For each selector in <var>result</var> that begins with a sequence of
    simple selectors that does not contain the <code><a
    href="#scope">:scope</a></code> pseudo-class, insert the simple selector
    <code><a href="#scope">:scope</a></code> followed by a descendant
    combinator at the beginning.

   <li>Return <var>result</var>.
  </ol>

  <div class=example>
   <p>For example, if the <a href="#scoped-selector-string">scoped selector
    string</a> is “<code>div div, :scope+p"</code>” the processing will
    result in the selector being equivalent to “<code>:scope div div,
    :scope+p</code>”</p>
  </div>

  <p>The steps to <dfn id=evaluate-a-selector>evaluate a selector</dfn> are
   as follows:

  <ol>
   <li>Let <var>selector group</var> be the selector input into this
    algotihm.

   <li>Let <var>reference nodes</var> be the reference nodes input into this
    algorithm.

   <li>Let <var title="">element</var> be the element being evaluated.

   <li>The <code><a href="#scope">:scope</a></code> pseudo class, if used in
    <var>selector group</var>, must match any node within the <var>reference
    nodes</var> collection.

   <li>If any selector in <var>selector group</var> matches <var
    title="">element</var>, return true. Otherwise, return false.
  </ol>

  <p>Selectors are evaluated against a given element in the context of the
   entire DOM tree in which the element is located. If the given group of
   selectors is <a
   href="http://www.w3.org/TR/css3-selectors/#Conformance">invalid</a> (<a
   href="#SELECT" rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, section
   13), the implementation <em class=ct>must</em> <a
   href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMException-SYNTAX_ERR">raise
   a <code>SYNTAX_ERR</code> exception</a> (<a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a>,
   section 1.4).

  <p>If the user agent also supports some level of CSS, the implementation
   <em class=ct>should</em> support the same set of selectors in both these
   APIs and CSS.

  <h3 id=processing-reference-nodes><span class=secno>6.4. </span>Processing
   Reference Nodes</h3>

  <p>The steps to <dfn id=determine-contextual-reference-nodes>determine
   contextual reference nodes</dfn> are as follows:

  <ol>
   <li>Let <var>input</var> be the value that is being processed, if any.

   <li>Let <var>result</var> be an intially empty collection of <code><a
    href="#dom-element">Element</a></code> nodes.

   <li>If the <var>input</var> is an <code><a
    href="#dom-element">Element</a></code> node, then that append that
    element to the <var>result</var> collection.

   <li>If <var>input</var> is a <code>NodeList</code> or
    <code>HTMLCollection</code>, then append each <code><a
    href="#dom-element">Element</a></code> node contained within it to the
    <var>result</var> collection.

   <li>If <var>input</var> is an <code>Array</code> or other object with
    indexable properties, then iterate through <var>input</var> to find and
    append each <code><a href="#dom-element">Element</a></code> node
    contained within it to the <var>result</var> collection.

   <li>If <var>results</var> is still an empty collection and the <a
    href="#context-node">context node</a> is an <code><a
    href="#dom-element">Element</a></code> node, append the <a
    href="#context-node">context node</a> to the <var>result</var>
    collection.

   <li>Otherwise, if <var>results</var> is still an empty collection and the
    <a href="#context-node">context node</a> is a <code>Document</code> node,
    then append the <code>documentElement</code> of the given document, if
    any, to the <var>result</var> collection.

   <li>Return <var>result</var>.
  </ol>

  <p class=note>The result may still be an empty collection at the end of
   that process.

  <h3 id=resolving-namespaces><span class=secno>6.5. </span>Resolving
   Namespaces</h3>

  <p>If the group of selectors include <a
   href="#namespace-prefix-needs-to-be-resolved"
   title=need-to-resolve>namespace prefixes that need to be resolved</a>, the
   implementation <em class=ct>must</em> <a
   href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMException-NAMESPACE_ERR">raise
   a <code>NAMESPACE_ERR</code> exception</a> (<a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a>,
   section 1.4).

  <p class=note>This specification does not provide support for resolving
   arbitrary namespace prefixes. However, support for a namespace prefix
   resolution mechanism may be considered for inclusion in a future version
   of this specification.

  <p>A <dfn id=namespace-prefix-needs-to-be-resolved
   title=need-to-resolve>namespace prefix needs to be resolved</dfn> if the
   namespace component is neither empty (e.g. <code>|div</code>),
   representing the null namespace, or an asterisk (e.g. <code>*|div</code>),
   representing any namespace. Since the asterisk or empty namespace prefix
   do not need to be resolved, implementations that support the namespace
   syntax in Selectors <em class=ct>must</em> support these. <a
   href="#SELECT" rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>

  <p class=note>Implementations that don't support the namespace syntax in
   Selectors would instead throw a <code>SYNTAX_ERR</code> because it would
   be treated as an invalid selector.

  <p>In addition to the terms defined in this specification, the terms
   defined in Selectors <a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a> and DOM Level 3 Core <a
   href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a> are
   also used.

  <h2 id=the-scope-pseudo-class><span class=secno>7. </span>The <dfn
   id=scope><code>:scope</code></dfn> Pseudo-Class</h2>

  <p class=issue>This section is expected to be moved to the Selectors Level
   4 specification when the CSSWG begins work. It is defined here only
   because it needs to be defined somewhere. Note that this has been called
   various names including <code>:reference</code> and <code>:context</code>
   in previous discussions.

  <p>A <dfn id=contextual-reference-element>contextual reference
   element</dfn> is a specified reference <code><a
   href="#dom-element">Element</a></code> node within the context in which a
   selector is being evaluated. There may be more than one such element in a
   given context.

  <p>The <code><a href="#scope">:scope</a></code> pseudo-class <em
   class=ct>must</em> match any element that is a <a
   href="#contextual-reference-element">contextual reference element</a>.

  <p>When a given element is being evaluated against a given selector in a
   given context, there may be one or more <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes specified. If there are no other <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes specified, and the element being evaluated belongs to a document,
   the root element of the document to which the element belongs is a <a
   href="#contextual-reference-element">contextual reference element</a>.
   Otherwise, there is no <a href="#contextual-reference-element">contextual
   reference element</a>.

  <p>Specifications intending for this pseudo-class to match specific
   elements other than the document's root element <em class=ct>must</em>
   define which elements are the <a
   href="#contextual-reference-element">contextual reference element</a>
   nodes.

  <h2 id=dom-feature-string><span class=secno>8. </span>DOM Feature String</h2>

  <p>DOM3 Core defines several methods for checking for interface support, or
   for obtaining implementations of interfaces, using <a
   href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMFeatures">feature
   strings</a> (<a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{!DOM-LEVEL-3-CORE}}--></a>,
   section 1.3.6). A DOM application can use these methods, each of which
   accept <var>feature</var> and <var>version</var> parameters, using the
   values "<code title="">Selectors-API</code>" and "<code>1.0</code>"
   (respectively).

  <p class=note>The version parameter has been intentionally left as
   "<code>1.0</code>". This is intended only as a way to detect the presence
   of some level of support, rather than being able claim support for a
   specific level of this API.

  <p>Conforming implementations <em class=ct>must</em> respond with a
   <code>true</code> value when the <code>hasFeature</code> method is queried
   with these values. Authors are cautioned, however, that implementations
   returning <code>true</code> might not be perfectly compliant, and that
   implementations returning <code>false</code> might well have support for
   features in this specification; in general, therefore, use of this method
   is discouraged.

  <h2 id=examples0><span class=secno>9. </span>Examples</h2>

  <p class=issue>Add more examples illustrating the use of the reference node
   and :scope selector, as well as the queryScopedSelector() and
   matchesSelector() methods.

  <div class=example>
   <p>The following examples make use of this sample XHTML document.</p>

   <pre>&lt;html xmlns="http://www.w3.org/1999/xhtml">
  &lt;head>
    &lt;title&gt;Selectors API Example&lt;/title&gt;
  &lt;/head>
  &lt;body>
    &lt;div id="foo"&gt;
      &lt;p class="warning"&gt;This is a sample warning&lt;/p&gt;
      &lt;p class="error"&gt;This is a sample error&lt;/p&gt;
    &lt;/div&gt;
    &lt;div id="bar"&gt;
      &lt;p&gt;...&lt;/p&gt;
    &lt;/div&gt;
  &lt;/body>
&lt;/html></pre>

   <p>The methods accept a group of selectors (comma separated) as the
    argument. The following example would select all <code>p</code> elements
    in the document that have a class of either "<code>error</code>" or
    "<code>warning</code>".</p>

   <pre>var alerts = document.querySelectorAll("p.warning, p.error");</pre>

   <p>The <code title=document-selectelement>querySelector()</code> methods
    also accept a group of selectors and they will return the first element
    (if any) that matches any of the selectors in the group.</p>

   <pre>var x = document.querySelector("#foo, #bar");</pre>

   <p><var>x</var> would contain the first element in the document with an ID
    of either <code>foo</code> or <code>bar</code>, or <code>null</code> if
    there is no such element. In the sample document above, it would select
    the <code>div</code> element with the ID of <code>foo</code> because it
    is first in document order. The order of the selectors used in the
    parameter has no effect and would have the same result if the order were
    reversed, as in:</p>

   <pre>var x = document.querySelector("#bar, #foo");</pre>

   <p>The methods can also be invoked on elements. In the following example,
    assume the event handler is registered on an element, and thus the method
    is invoked on the target element of the event.</p>

   <pre>function handle(evt) {
  var x = evt.target.querySelector("span");
  ...
  // Do something with x
}</pre>

   <p>Even though the method is invoked on an element, selectors are still
    evaluated in the context of the entire document. In the following
    example, the method will still match the <code>div</code> element's child
    <code>p</code> element, even though the <code>body</code> element is not
    a descendant of the <code>div</code> element itself.</p>

   <pre>var div = document.getElementById("bar");
var p = div.querySelector("body p");</pre>

   <p>Given this sample fragment that contains a list as a navigation menu:</p>

   <pre>&lt;ul class="nav"&gt;
  &lt;li&gt;&lt;a href="/"&gt;Home&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href="/products"&gt;Products&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href="/about"&gt;About&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;</pre>

   <p>The following example selects all the <code>li</code> elements and
    demonstrates how to iterate through the collection in a
    <code>NodeList</code>.</p>

   <pre>var lis = document.querySelectorAll("ul.nav&gt;li");
for (var i = 0; i &lt; lis.length; i++) {
  process(lis.item(i));
}</pre>

   <p>In ECMAScript, the language binding also allows <code>NodeList</code>s
    to be addressed using the array notation, so that loop could be rewritten
    like this:</p>

   <pre>for (var i = 0; i &lt; lis.length; i++) {
  process(lis[i]);
}</pre>

   <p>Since the <code>NodeList</code> objects returned by these methods are
    not live, changes to the DOM do not affect the content of the list.
    Consider the <code>process()</code> function called in the previous
    examples is defined as follows:</p>

   <pre>function process(elmt) {
  elmt.parentNode.removeChild(elmt);
}</pre>

   <p>This would cause each selected element to be removed from the DOM, but
    each element will remain in the <code>NodeList</code>. If the list were a
    live <code>NodeList</code>, removing an item from the DOM would also
    remove the element from the list and adjust the indexes of subsequent
    elements. That would have adverse effects upon the loop because not all
    selected elements would be processed.</p>

   <p>In documents comprising elements from multiple namespaces, it's
    possible that some elements from different namespaces share the same
    local name. Since this API does not natively support a namespace
    resolution mechanism for selectors, obtaining a list of such elements
    from a specific namespace, excluding all others, requires additional
    processing to filter the result. The following example illustrates a
    document containing <code>video</code> elements from both the SVG and
    XHTML namespaces.</p>

   <pre>&lt;svg id=&quot;svg1&quot; xmlns=&quot;http://www.w3.org/2000/svg&quot;
               xmlns:xlink=&quot;http://www.w3.org/1999/xlink&quot;&gt;
  &lt;video id=&quot;svgvideo1&quot; xlink:href=&quot;myvideo.ogg&quot; width=&quot;320&quot; height=&quot;240&quot;/&gt;
  &lt;foreignObject width=&quot;100&quot; height=&quot;100&quot;&gt;
    &lt;video id=&quot;htmlvideo1&quot; src=&quot;myvideo.ogg&quot; xmlns=&quot;http://www.w3.org/1999/xhtml&quot;&gt;No video1&lt;/video&gt;
  &lt;/foreignObject&gt;
&lt;/svg&gt;</pre>

   <p>The following script demonstrates how to first select the
    <code>video</code> elements and then filter out the unwanted elements
    based on their namespace.</p>

   <pre>var list = document.querySelectorAll("svg video");
var result = new Array();
var svgns = "http://www.w3.org/2000/svg"

for(var i = 0; i < elms.length; i++) {
  if(list[i].namespaceURI == svgns) {
    result.push(elms[i]);
  }
}</pre>
  </div>

  <h2 class=no-num id=references>References</h2>

  <h3 class=no-num id=normative-references>Normative references</h3>
  <!--begin-normative-->
  <!-- Sorted by label -->

  <dl class=bibliography>
   <dt style="display: none"><!-- keeps the doc valid if the DL is empty -->
    <!---->

   <dt id=DOM-LEVEL-3-CORE>[DOM-LEVEL-3-CORE]

   <dd>Gavin Nicol; et al. <a
    href="http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407"><cite>Document
    Object Model (DOM) Level 3 Core Specification.</cite></a> 7 April 2004.
    W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407">http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407</a>
    </dd>
   <!---->

   <dt id=RFC2119>[RFC2119]

   <dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key
    words for use in RFCs to Indicate Requirement Levels.</cite></a> Internet
    RFC 2119. URL: <a
    href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
    </dd>
   <!---->

   <dt id=SELECT>[SELECT]

   <dd>Tantek &#199;elik; et al. <a
    href="http://www.w3.org/TR/2009/WD-css3-selectors-20090310"><cite>Selectors
    Level 3.</cite></a> 10 March 2009. W3C Working Draft. (Work in progress.)
    URL: <a
    href="http://www.w3.org/TR/2009/WD-css3-selectors-20090310">http://www.w3.org/TR/2009/WD-css3-selectors-20090310</a>
    </dd>
   <!---->

   <dt id=WEBIDL>[WEBIDL]

   <dd>Cameron McCormack. <a
    href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web
    IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.)
    URL: <a
    href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a>
    </dd>
   <!---->
  </dl>
  <!--end-normative-->

  <h3 class=no-num id=informative-references>Informative references</h3>
  <!--begin-informative-->
  <!-- Sorted by label -->

  <dl class=bibliography>
   <dt style="display: none"><!-- keeps the doc valid if the DL is empty -->
    <!---->

   <dt id=CSS21>[CSS21]

   <dd>Bert Bos; et al. <a
    href="http://www.w3.org/TR/2009/CR-CSS2-20090908"><cite>Cascading Style
    Sheets Level 2 Revision 1 (CSS 2.1) Specification.</cite></a> 8 September
    2009. W3C Candidate Recommendation. (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2009/CR-CSS2-20090908">http://www.w3.org/TR/2009/CR-CSS2-20090908</a>
    </dd>
   <!---->

   <dt id=DOM-LEVEL-2-STYLE>[DOM-LEVEL-2-STYLE]

   <dd>Chris Wilson; Philippe Le H&#233;garet; Vidur Apparao. <a
    href="http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113"><cite>Document
    Object Model (DOM) Level 2 Style Specification.</cite></a> 13 November
    2000. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113">http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113</a>
    </dd>
   <!---->

   <dt id=ECMA-262>[ECMA-262]

   <dd><a
    href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"><cite>ECMAScript
    Language Specification, Third Edition.</cite></a> December 1999. URL: <a
    href="http://www.ecma-international.org/publications/standards/Ecma-262.htm">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a>
    </dd>
   <!---->
  </dl>
  <!--end-informative-->

  <h2 class=no-num id=acknowledgements>Acknowledgements</h2>

  <p>The editors would like to thank to the following people who have
   contributed to this specification (ordered on first name):

  <p>Adam van den Hoven, Alan Gresley, Alex Russell, Björn Höhrmann, Boris
   Zbarsky, Cameron McCormack, Charles McCathieNevile, Chris Wilson,
   Christophe Jolif, Daniel Glazman, Daniel Schierbeck, Dave Massy, David
   "liorean" Andersson, David Håsäther, Dean Jackson, Doug Schepers, Erik
   Dahlström, Francois Remy, Garret Smith, Hallvord R. M. Steen, Ian
   Hickson, Ivan Enderlin, Jean-Yves Bitterlich, Jim Ley, João Eiras, John
   Resig, Jon Ferraiolo, Jonas Sicking, Jorgen Horstink, Karl Dubost,
   Kartikaya Gupta, L. David Baron, Maciej Stachowiak, Magnus Kristiansen,
   Martijn, Masataka Yakura, Mihai Sucan, Mohamed Zergaoui, Nicholas C.
   Zakas, Nicolas Mendoza, Philip Taylor, Robert Sayre, Robin Berjon, Sander,
   Sergey Ilinsky, Simon Pieters, Steven Pemberton, Tarquin Wilton-Jones,
   Travis Leithead, and William J. Edney

  <p>Thanks to all those who have helped to improve this specification by
   sending suggestions and corrections.