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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">

<html lang=en>
 <head>
  <title>Selectors Level 4</title>
  <link href=default.css rel=stylesheet type="text/css">

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   <p><a href="http://www.w3.org/"><img alt=W3C height=48
    src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->

   <h1 id=title>Selectors Level 4</h1>

   <h2 class="no-num no-toc" id=longstatus-date>W3C Working Draft 29
    September 2011</h2>

   <dl>
    <dt>This version:

    <dd><a href="http://www.w3.org/TR/2011/WD-selectors4-20110929/">
     http://www.w3.org/TR/2011/WD-selectors4-20110929/</a>

    <dt>Editor's draft:

    <dd><a href="http://dev.w3.org/csswg/selectors4/">
     http://dev.w3.org/csswg/selectors4/</a>

    <dt>Latest version of Selectors Level 4:

    <dd><a href="http://www.w3.org/TR/selectors4/">
     http://www.w3.org/TR/selectors4/</a>

    <dt>Latest Selectors specification:

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

    <dt>Previous version:

    <dd>-

    <dt>Editors:

    <dd class=vcard><a class="url fn"
     href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
     (Mozilla)

    <dt>Previous Editors:

    <dd class=vcard><a class="url fn" href="http://www.tantek.com/"
     lang=tr>Tantek &Ccedil;elik</a> (Microsoft)

    <dd class=vcard><span class=fn>Daniel Glazman</span> (Disruptive
     Innovations SARL)

    <dd class=vcard><span class=fn>Ian Hickson</span> (Opera Softare ASA)

    <dd class=vcard><span class=fn>Peter Linss</span> (Netscape/AOL)

    <dd class=vcard><span class=fn>John Williams</span> (Quark, Inc.)
   </dl>
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    rel=license>Copyright</a> &copy; 2011 <a
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    Consortium">W3C</acronym></a><sup>&reg;</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>
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    use</a> rules apply.</p>
   <!--end-copyright-->
   <hr title="Separator for header">
  </div>

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

  <p><em>Selectors</em> are patterns that match against elements in a tree,
   and as such form one of several technologies that can be used to select
   nodes in an XML document. Selectors have been optimized for use with HTML
   and XML, and are designed to be usable in performance-critical code. They
   are a core component of <abbr title="Cascading Style Sheets">CSS</abbr>
   (Cascading Style Sheets), which uses Selectors to bind style properties to
   elements in the document.

  <p>Selectors Level 4 describes the selectors that already exist in <a
   href="#SELECT" rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>, and further
   introduces new selectors for CSS and other languages that may need them.

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

  <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 at http://www.w3.org/TR/.</a></em>

  <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>The (<a
   href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
   mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
   <a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
   for discussion of this specification. When sending e-mail, please put the
   text &#8220;selectors4&#8221; in the subject, preferably like this:
   &#8220;[<!---->selectors4<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

  <p>This document was produced by the <a
   href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
   the <a href="http://www.w3.org/Style/">Style Activity</a>).

  <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/32061/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>.</p>
  <!--end-status-->

  <p><strong>This module is an early-stage Working Draft. If you are looking
   for a stable Selectors specification, use <a
   href="http://www.w3.org/TR/css3-selectors/">Selectors 3</a>.</strong> Read
   the <a href="http://www.w3.org/TR/CSS/">CSS Snapshot</a> for an overview
   of the CSS development process. See the <a href="#overview">Selectors
   Overview</a> for a summary of additions to level 3.

  <p>This is the first public Working Draft of this new specification.

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

  <ul class=toc>
   <li><a href="#context"><span class=secno>1. </span> Introduction</a>
    <ul class=toc>
     <li><a href="#placement"><span class=secno>1.1. </span>Module
      Interactions</a>
    </ul>

   <li><a href="#overview"><span class=secno>2. </span> Selectors
    Overview</a>

   <li><a href="#syntax"><span class=secno>3. </span> Selector Syntax and
    Structure</a>
    <ul class=toc>
     <li><a href="#structure"><span class=secno>3.1. </span> Structure and
      Terminology</a>

     <li><a href="#subject"><span class=secno>3.2. </span> Determining the
      Subject of a Selector</a>

     <li><a href="#pseudo-classes"><span class=secno>3.3. </span>
      Pseudo-classes</a>

     <li><a href="#pseudo-elements"><span class=secno>3.4.
      </span>Pseudo-elements</a>

     <li><a href="#case-sensitive"><span class=secno>3.5. </span> Characters
      and case sensitivity</a>

     <li><a href="#namespaces"><span class=secno>3.6. </span> Namespaces</a>

     <li><a href="#invalid"><span class=secno>3.7. </span> Invalid Selectors
      and Error Handling</a>
    </ul>

   <li><a href="#logical-combination"><span class=secno>4. </span> Logical
    Combinations</a>
    <ul class=toc>
     <li><a href="#grouping"><span class=secno>4.1. </span> Selector
      Lists</a>

     <li><a href="#matches"><span class=secno>4.2. </span> The Matches-Any
      Pseudo-class: &lsquo;<code class=css>:matches()</code>&rsquo;</a>

     <li><a href="#negation"><span class=secno>4.3. </span> The Negation
      Pseudo-class: &lsquo;<code class=css>:not()</code>&rsquo;</a>
    </ul>

   <li><a href="#elemental-selectors"><span class=secno>5. </span> Elemental
    selectors</a>
    <ul class=toc>
     <li><a href="#type-selectors"><span class=secno>5.1. </span> Type
      selector</a>
      <ul class=toc>
       <li><a href="#typenmsp"><span class=secno>5.1.1. </span> Type
        selectors and namespaces</a>
      </ul>

     <li><a href="#universal-selector"><span class=secno>5.2. </span>
      Universal selector </a>
      <ul class=toc>
       <li><a href="#univnmsp"><span class=secno>5.2.1. </span> Universal
        selector and namespaces</a>
      </ul>
    </ul>

   <li><a href="#attribute-selectors"><span class=secno>6. </span> Attribute
    selectors</a>
    <ul class=toc>
     <li><a href="#attribute-representation"><span class=secno>6.1. </span>
      Attribute presence and value selectors</a>

     <li><a href="#attribute-substrings"><span class=secno>6.2. </span>
      Substring matching attribute selectors</a>

     <li><a href="#attribute-case"><span class=secno>6.3. </span>
      Case-sensitivity</a>

     <li><a href="#attrnmsp"><span class=secno>6.4. </span> Attribute
      selectors and namespaces</a>

     <li><a href="#def-values"><span class=secno>6.5. </span> Default
      attribute values in DTDs</a>

     <li><a href="#class-html"><span class=secno>6.6. </span> Class
      selectors</a>

     <li><a href="#id-selectors"><span class=secno>6.7. </span> ID
      selectors</a>
    </ul>

   <li><a href="#location"><span class=secno>7. </span> Location
    Pseudo-classes</a>
    <ul class=toc>
     <li><a href="#any-link-pseudo"><span class=secno>7.1. </span> The
      hyperlink pseudo-class: &lsquo;<code
      class=css>:any-link</code>&rsquo;</a>

     <li><a href="#link"><span class=secno>7.2. </span> The link history
      pseudo-classes: &lsquo;<code class=css>:link</code>&rsquo; and
      &lsquo;<code class=css>:visited</code>&rsquo;</a>

     <li><a href="#local-pseudo"><span class=secno>7.3. </span> The local
      link pseudo-class &lsquo;<code class=css>:local-link</code>&rsquo;</a>

     <li><a href="#target-pseudo"><span class=secno>7.4. </span> The target
      pseudo-class &lsquo;<code class=css>:target</code>&rsquo;</a>

     <li><a href="#scope-pseudo"><span class=secno>7.5. </span> The
      contextual reference element pseudo-class &lsquo;<code
      class=css>:scope</code>&rsquo;</a>
    </ul>

   <li><a href="#useraction-pseudos"><span class=secno>8. </span> User Action
    Pseudo-classes</a>
    <ul class=toc>
     <li><a href="#hover-pseudo"><span class=secno>8.1. </span> The pointer
      hover pseudo-class &lsquo;<code class=css>:hover</code>&rsquo;</a>

     <li><a href="#active-pseudo"><span class=secno>8.2. </span> The
      activation pseudo-class &lsquo;<code
      class=css>:active</code>&rsquo;</a>

     <li><a href="#focus-pseudo"><span class=secno>8.3. </span> The input
      focus pseudo-class &lsquo;<code class=css>:focus</code>&rsquo;</a>
    </ul>

   <li><a href="#time-pseudos"><span class=secno>9. </span> Time-dimensional
    Pseudo-classes</a>
    <ul class=toc>
     <li><a href="#current-pseudo"><span class=secno>9.1. </span> The
      current-element pseudo-class &lsquo;<code
      class=css>:current</code>&rsquo;</a>

     <li><a href="#past-pseudo"><span class=secno>9.2. </span> The
      past-element pseudo-class &lsquo;<code
      class=css>:past</code>&rsquo;</a>

     <li><a href="#future-pseudo"><span class=secno>9.3. </span> The
      future-element pseudo-class &lsquo;<code
      class=css>:future</code>&rsquo;</a>
    </ul>

   <li><a href="#linguistic-pseudos"><span class=secno>10. </span> Linguistic
    Pseudo-classes</a>
    <ul class=toc>
     <li><a href="#dir-pseudo"><span class=secno>10.1. </span> The
      directionality pseudo-class &lsquo;<code
      class=css>:dir()</code>&rsquo;</a>

     <li><a href="#lang-pseudo"><span class=secno>10.2. </span> The language
      pseudo-class &lsquo;<code class=css>:lang</code>&rsquo;</a>
    </ul>

   <li><a href="#ui-states-pseudos"><span class=secno>11. </span> The UI
    states pseudo-classes</a>
    <ul class=toc>
     <li><a href="#enableddisabled"><span class=secno>11.1. </span> The
      &lsquo;<code class=css>:enabled</code>&rsquo; and &lsquo;<code
      class=css>:disabled</code>&rsquo; pseudo-classes</a>

     <li><a href="#checked"><span class=secno>11.2. </span> The
      selected-option pseudo-class &lsquo;<code
      class=css>:checked</code>&rsquo;</a>

     <li><a href="#indeterminate"><span class=secno>11.3. </span> The
      indeterminate-value pseudo-class &lsquo;<code
      class=css>:indeterminate</code>&rsquo;</a>

     <li><a href="#default-pseudo"><span class=secno>11.4. </span> The
      default option pseudo-class &lsquo;<code
      class=css>:default</code>&rsquo;</a>

     <li><a href="#validity-pseudos"><span class=secno>11.5. </span> The
      validity pseudo-classes &lsquo;<code class=css>:valid</code>&rsquo; and
      &lsquo;<code class=css>:invalid</code>&rsquo;</a>

     <li><a href="#range-pseudos"><span class=secno>11.6. </span> The range
      pseudo-classes &lsquo;<code class=css>:in-range</code>&rsquo; and
      &lsquo;<code class=css>:out-of-range</code>&rsquo;</a>

     <li><a href="#opt-pseudos"><span class=secno>11.7. </span> The
      optionality pseudo-classes &lsquo;<code
      class=css>:required</code>&rsquo; and &lsquo;<code
      class=css>:optional</code>&rsquo;</a>

     <li><a href="#rw-pseudos"><span class=secno>11.8. </span> The mutability
      pseudo-classes &lsquo;<code class=css>:read-only</code>&rsquo; and
      &lsquo;<code class=css>:read-write</code>&rsquo;</a>
    </ul>

   <li><a href="#structural-pseudos"><span class=secno>12. </span>
    Tree-Structural pseudo-classes</a>
    <ul class=toc>
     <li><a href="#root-pseudo"><span class=secno>12.1. </span> &lsquo;<code
      class=css>:root</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-child-pseudo"><span class=secno>12.2. </span>
      &lsquo;<code class=css>:nth-child()</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-last-child-pseudo"><span class=secno>12.3. </span>
      &lsquo;<code class=css>:nth-last-child()</code>&rsquo; pseudo-class</a>
      

     <li><a href="#nth-of-type-pseudo"><span class=secno>12.4. </span>
      &lsquo;<code class=css>:nth-of-type()</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-last-of-type-pseudo"><span class=secno>12.5. </span>
      &lsquo;<code class=css>:nth-last-of-type()</code>&rsquo;
      pseudo-class</a>

     <li><a href="#nth-match"><span class=secno>12.6. </span> &lsquo;<code
      class=css>:nth-match()</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-last-match"><span class=secno>12.7. </span>
      &lsquo;<code class=css>:nth-last-match()</code>&rsquo; pseudo-class</a>
      

     <li><a href="#first-child-pseudo"><span class=secno>12.8. </span>
      &lsquo;<code class=css>:first-child</code>&rsquo; pseudo-class</a>

     <li><a href="#last-child-pseudo"><span class=secno>12.9. </span>
      &lsquo;<code class=css>:last-child</code>&rsquo; pseudo-class</a>

     <li><a href="#first-of-type-pseudo"><span class=secno>12.10. </span>
      &lsquo;<code class=css>:first-of-type</code>&rsquo; pseudo-class</a>

     <li><a href="#last-of-type-pseudo"><span class=secno>12.11. </span>
      &lsquo;<code class=css>:last-of-type</code>&rsquo; pseudo-class</a>

     <li><a href="#only-child-pseudo"><span class=secno>12.12. </span>
      &lsquo;<code class=css>:only-child</code>&rsquo; pseudo-class</a>

     <li><a href="#only-of-type-pseudo"><span class=secno>12.13. </span>
      &lsquo;<code class=css>:only-of-type</code>&rsquo; pseudo-class</a>

     <li><a href="#empty-pseudo"><span class=secno>12.14. </span>
      &lsquo;<code class=css>:empty</code>&rsquo; pseudo-class</a>
    </ul>

   <li><a href="#table-pseudos"><span class=secno>13. </span> Grid-Structural
    Selectors</a>
    <ul class=toc>
     <li><a href="#column-pseudo"><span class=secno>13.1. </span>
      &lsquo;<code class=css>:column()</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-column-pseudo"><span class=secno>13.2. </span>
      &lsquo;<code class=css>:nth-column()</code>&rsquo; pseudo-class</a>

     <li><a href="#nth-last-column-pseudo"><span class=secno>13.3. </span>
      &lsquo;<code class=css>:nth-last-column()</code>&rsquo;
      pseudo-class</a>
    </ul>

   <li><a href="#combinators"><span class=secno>14. </span> Combinators</a>
    <ul class=toc>
     <li><a href="#descendant-combinators"><span class=secno>14.1. </span>
      Descendant combinator</a>

     <li><a href="#child-combinators"><span class=secno>14.2. </span> Child
      combinators</a>

     <li><a href="#adjacent-sibling-combinators"><span class=secno>14.3.
      </span> Adjacent sibling combinator</a>

     <li><a href="#general-sibling-combinators"><span class=secno>14.4.
      </span> General sibling combinator</a>

     <li><a href="#idref-combinators"><span class=secno>14.5. </span>
      Reference combinators</a>
    </ul>

   <li><a href="#specificity"><span class=secno>15. </span> Calculating a
    selector's specificity</a>

   <li><a href="#formal-syntax"><span class=secno>16. </span> Formal
    Syntax</a>
    <ul class=toc>
     <li><a href="#grammar"><span class=secno>16.1. </span> Grammar</a>

     <li><a href="#lex"><span class=secno>16.2. </span> Lexical scanner</a>
    </ul>

   <li><a href="#profiling"><span class=secno>17. </span> Profiles</a>
    <ul class=toc>
     <li><a href="#css-profiles"><span class=secno>17.1. </span> CSS
      Profiles</a>

     <li><a href="#stts-profile"><span class=secno>17.2. </span> STTS
      Profiles</a>
    </ul>

   <li><a href="#conformance"><span class=secno>18. </span> Conformance</a>
    <ul class=toc>
     <li><a href="#conventions"><span class=secno>18.1. </span>Document
      Conventions</a>

     <li><a href="#conformance-classes"><span class=secno>18.2. </span>
      Conformance Classes</a>

     <li><a href="#partial"><span class=secno>18.3. </span> Partial
      Implementations</a>

     <li><a href="#experimental"><span class=secno>18.4. </span> Experimental
      Implementations</a>
    </ul>

   <li><a href="#acknowledgements"><span class=secno>19. </span>
    Acknowledgements</a>

   <li><a href="#references"><span class=secno>20. </span> References</a>
    <ul class=toc>
     <li><a href="#normative-references"><span class=secno>20.1. </span>
      Normative References</a>

     <li><a href="#informative-references"><span class=secno>20.2. </span>
      Informative References</a>
    </ul>
  </ul>
  <!--end-toc-->

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

  <p><em>This section is not normative.</em>

  <p>Selectors define the following function for elements in a tree
   structure:

  <pre>expression &#x2217; element &rarr; boolean</pre>

  <p>That is, given an element and a selector, this specification defines
   whether that element matches the selector.

  <p>These expressions can also be used, for instance, to select a set of
   elements, or a single element from a set of elements, by evaluating the
   expression across all the elements in a subtree. <abbr title="Simple Tree
   Transformation Sheets">STTS</abbr> (Simple Tree Transformation Sheets), a
   language for transforming XML trees, uses this mechanism. <a href="#STTS3"
   rel=biblioentry>[STTS3]<!--{{STTS3}}--></a>

  <p>Selectors Levels 1, 2, and 3 are defined as the subsets of selector
   functionality defined in the <a
   href="http://www.w3.org/TR/REC-CSS1">CSS1</a>, <a
   href="http://www.w3.org/TR/CSS21/">CSS2.1</a>, and <a
   href="http://www.w3.org/TR/css3-selectors/">Selectors Level 3</a>
   specifications, respectively. This module defines Selectors Level 4.

  <h3 id=placement><span class=secno>1.1. </span>Module Interactions</h3>

  <p>This module replaces the definitions for, and extends the set of
   selectors defined for CSS in <a href="#SELECT"
   rel=biblioentry>[SELECT]<!--{{SELECT}}--></a> and <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{CSS21}}--></a>.

  <p>Pseudo-element selectors, which define abstract elements in a rendering
   tree, are not part of this specification: their generic syntax is
   described here, but, due to their close integration with the rendering
   model and irrelevance to other uses such as DOM queries, they will be
   defined in other modules.

  <h2 id=overview><span class=secno>2. </span> Selectors Overview</h2>

  <p><em>This section is non-normative, as it merely summarizes the following
   sections.</em>

  <p>A Selector represents a structure. This structure can be used as a
   condition (e.g. in a CSS rule) that determines which elements a selector
   matches in the document tree, or as a flat description of the HTML or XML
   fragment corresponding to that structure.

  <p>Selectors may range from simple element names to rich contextual
   representations.

  <p>The following table summarizes the Selector syntax:

  <table class=data><col class=pattern><col class=meaning><col
   class=section><col class=level>
   <thead>
    <tr>
     <th>Pattern

     <th>Meaning

     <th>Section

     <th>Level

   <tbody>
    <tr>
     <td><code>*</code>

     <td>any element

     <td><a href="#universal-selector">Universal selector</a>

     <td>2

    <tr>
     <td><code>E</code>

     <td>an element of type E

     <td><a href="#type-selectors">Type selector</a>

     <td>1

   <tbody>
    <tr>
     <td><code>E:not(<var>s</var>)</code>

     <td>an E element that does not match simple selector <var>s</var>

     <td><a href="#negation">Negation pseudo-class</a>

     <td>3

    <tr>
     <td><code>E:not(<var>s1</var>, <var>s2</var>)</code>

     <td>an E element that does not match either compound selector
      <var>s1</var> or compound selector <var>s2</var>

     <td><a href="#negation">Negation pseudo-class</a>

     <td>4

    <tr>
     <td><code>E:matches(<var>s1</var>, <var>s2</var>)</code>

     <td>an E element that matches compound selector <var>s1</var> and/or
      compound selector <var>s2</var>

     <td><a href="#matches">Matches-any pseudo-class</a>

     <td>4

   <tbody>
    <tr>
     <td><code>E.warning</code>

     <td>an E element belonging to the class <code>warning</code> (the
      document language specifies how class is determined).

     <td><a href="#class-html">Class selectors</a>

     <td>1

    <tr>
     <td><code>E#myid</code>

     <td>an E element with ID equal to <code>myid</code>.

     <td><a href="#id-selectors">ID selectors</a>

     <td>1

    <tr>
     <td><code>E[foo]</code>

     <td>an E element with a <code>foo</code> attribute

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>2

    <tr>
     <td><code>E[foo="bar"]</code>

     <td>an E element whose <code>foo</code> attribute value is exactly equal
      to <code>bar</code>

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>2

    <tr>
     <td><code>E[foo="bar" i]</code>

     <td>an E element whose <code>foo</code> attribute value is exactly equal
      to any (ASCII-range) case-permutation of <code>bar</code>

     <td><a href="#attribute-case">Attribute selectors: Case-sensitivity</a>

     <td>4

    <tr>
     <td><code>E[foo~="bar"]</code>

     <td>an E element whose <code>foo</code> attribute value is a list of
      whitespace-separated values, one of which is exactly equal to
      <code>bar</code>

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>2

    <tr>
     <td><code>E[foo^="bar"]</code>

     <td>an E element whose <code>foo</code> attribute value begins exactly
      with the string "bar"

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>3

    <tr>
     <td><code>E[foo$="bar"]</code>

     <td>an E element whose <code>foo</code> attribute value ends exactly
      with the string <code>bar</code>

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>3

    <tr>
     <td><code>E[foo*="bar"]</code>

     <td>an E element whose <code>foo</code> attribute value contains the
      substring <code>bar</code>

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>3

    <tr>
     <td><code>E[foo|="en"]</code>

     <td>an E element whose <code>foo</code> attribute value is a
      hyphen-separated list of values beginning with <code>en</code>

     <td><a href="#attribute-selectors">Attribute selectors</a>

     <td>2

   <tbody>
    <tr>
     <td><code>E:dir(ltr)</code>

     <td>an element of type E in with left-to-right directionality (the
      document language specifies how directionality is determined)

     <td><a href="#dir-pseudo">The :dir() pseudo-class</a>

     <td>2

    <tr>
     <td><code>E:lang(fr)</code>

     <td>an element of type E in language "fr" (the document language
      specifies how language is determined)

     <td><a href="#lang-pseudo">The :lang() pseudo-class</a>

     <td>2

   <tbody>
    <tr>
     <td><code>E:any-link</code>

     <td>an E element being the source anchor of a hyperlink

     <td><a href="#any-link-pseudo">The hyperlink pseudo-class</a>

     <td>1

    <tr>
     <td><code>E:link</code>

     <td>an E element being the source anchor of a hyperlink of which the
      target is not yet visited

     <td><a href="#link">The link history pseudo-classes</a>

     <td>1

    <tr>
     <td><code>E:visited</code>

     <td>an E element being the source anchor of a hyperlink of which the
      target is already visited

     <td><a href="#link">The link history pseudo-classes</a>

     <td>1

    <tr>
     <td><code>E:local-link</code>

     <td>an E element being the source anchor of a hyperlink of which the
      target is the current document

     <td><a href="#local-pseudo">The local link pseudo-class</a>

     <td>4

    <tr>
     <td><code>E:local-link(0)</code>

     <td>an E element being the source anchor of a hyperlink of which the
      target is within the current domain

     <td><a href="#local-pseudo">The local link pseudo-class</a>

     <td>4

    <tr>
     <td><code>E:target</code>

     <td>an E element being the target of the referring URI

     <td><a href="#target-pseudo">The target pseudo-class</a>

     <td>3

    <tr>
     <td><code>E:scope</code>

     <td>an E element being a designated contextual reference element

     <td><a href="#scope-pseudo">The scope pseudo-class</a>

     <td>3

   <tbody>
    <tr>
     <td><code>E:current</code>

     <td>an E element that is currently presented in a time-dimensional
      canvas

     <td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:current(<var>s</var></code>

     <td>an E element that is the deepest <code>:current</code> element that
      matches selector <var>s</var>

     <td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:past</code>

     <td>an E element that is in the past in a time-dimensional canvas

     <td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:future</code>

     <td>an E element that is in the future in a time-dimensional canvas

     <td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>

     <td>4

   <tbody>
    <tr>
     <td><code>E:active</code>

     <td>an E element that is in an activated state

     <td><a href="#useraction-pseudos">The user action pseudo-classes</a>

     <td>1

    <tr>
     <td><code>E:hover</code>

     <td>an E element that is under the cursor, or that has a descendant
      under the cursor

     <td><a href="#useraction-pseudos">The user action pseudo-classes</a>

     <td>2

    <tr>
     <td><code>E:focus</code>

     <td>an E element that has user input focus

     <td><a href="#useraction-pseudos">The user action pseudo-classes</a>

     <td>2

    <tr>
     <td><code>E:enabled<br>
      E:disabled</code>

     <td>a user interface element E that is enabled or disabled, respectively
      

     <td><a href="#enableddisabled">The :enabled and :disabled
      pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:checked</code>

     <td>a user interface element E that is checked/selected (for instance a
      radio-button or checkbox)

     <td><a href="#checked">The selected-option pseudo-class</a>

     <td>3

    <tr>
     <td><code>E:indeterminate</code>

     <td>a user interface element E that is in an indeterminate state
      (neither checked nor unchecked)

     <td><a href="#indeterminate">The indeterminate-value pseudo-class</a>

     <td>4

    <tr>
     <td><code>E:default</code>

     <td>a user interface element E that

     <td><a href="#default-pseudo">The default option pseudo-class
      :default</a>

     <td>3-UI/4

    <tr>
     <td><code>E:in-range</code><br>
      <code>E:out-of-range</code>

     <td>a user interface element E that

     <td><a href="#range-pseudos">The validity pseudo-classes</a>

     <td>3-UI/4

    <tr>
     <td><code>E:required</code><br>
      <code>E:optional</code>

     <td>a user interface element E that

     <td><a href="#opt-pseudos">The optionality pseudo-classes</a>

     <td>3-UI/4

    <tr>
     <td><code>E:read-only</code><br>
      <code>E:read-write</code>

     <td>a user interface element E that

     <td><a href="#rw-pseudos">The mutability pseudo-classes</a>

     <td>3-UI/4

   <tbody>
    <tr>
     <td><code>E:root</code>

     <td>an E element, root of the document

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:empty</code>

     <td>an E element that has no children (not even text nodes)

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:first-child</code>

     <td>an E element, first child of its parent

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>2

    <tr>
     <td><code>E:nth-child(<var>n</var>)</code>

     <td>an E element, the <var>n</var>-th child of its parent

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:last-child</code>

     <td>an E element, last child of its parent

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:nth-last-child(<var>n</var>)</code>

     <td>an E element, the <var>n</var>-th child of its parent, counting from
      the last one

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:only-child</code>

     <td>an E element, only child of its parent

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:first-of-type</code>

     <td>an E element, first sibling of its type

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:nth-of-type(<var>n</var>)</code>

     <td>an E element, the <var>n</var>-th sibling of its type

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:last-of-type</code>

     <td>an E element, last sibling of its type

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:nth-last-of-type(<var>n</var>)</code>

     <td>an E element, the <var>n</var>-th sibling of its type, counting from
      the last one

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:only-of-type</code>

     <td>an E element, only sibling of its type

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>3

    <tr>
     <td><code>E:nth-match(<var>n</var> of <a
      href="#selector"><var>selector</var></a>)</code>

     <td>an E element, the <var>n</var>-th sibling matching <a
      href="#selector"><var>selector</var></a>

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:nth-match(<var>n</var> of <a
      href="#selector"><var>selector</var></a>)</code>

     <td>an E element, the <var>n</var>-th sibling matching <a
      href="#selector"><var>selector</var></a>

     <td><a href="#structural-pseudos">Structural pseudo-classes</a>

     <td>4

   <tbody>
    <tr>
     <td><code>E:column(<a href="#selector"><var>selector</var></a>)</code>

     <td>an E element that represents a cell in a grid/table belonging to a
      column represented by an element that matches <a
      href="#selector"><var>selector</var></a>

     <td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:nth-column(<var>n</var>)</code>

     <td>an E element that represents a cell belonging to the <var>n</var>th
      column in a grid/table

     <td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>

     <td>4

    <tr>
     <td><code>E:nth-last-column(<var>n</var>)</code>

     <td>an E element that represents a cell belonging to the <var>n</var>th
      column in a grid/table, counting from the last one

     <td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>

     <td>4

   <tbody>
    <tr>
     <td><code>E F</code>

     <td>an F element descendant of an E element

     <td><a href="#descendant-combinators">Descendant combinator</a>

     <td>1

    <tr>
     <td><code>E &gt; F</code>

     <td>an F element child of an E element

     <td><a href="#child-combinators">Child combinator</a>

     <td>2

    <tr>
     <td><code>E + F</code>

     <td>an F element immediately preceded by an E element

     <td><a href="#adjacent-sibling-combinators">Adjacent sibling
      combinator</a>

     <td>2

    <tr>
     <td><code>E ~ F</code>

     <td>an F element preceded by an E element

     <td><a href="#general-sibling-combinators">General sibling
      combinator</a>

     <td>3

    <tr>
     <td><code>E /foo/ F</code>

     <td>an F element ID-referenced by an E element's <code>foo</code>
      attribute

     <td><a href="#idref-combinators">Reference combinator</a>

     <td>4

    <tr>
     <td><code>$E &gt; F</code>

     <td>an E element parent of an E element

     <td><a href="#subject">Determining the subject of a selector</a> + <a
      href="#child-combinators">Child combinator</a>

     <td>4
  </table>

  <p>The meaning of each selector is derived from the table above by
   prepending "matches" to the contents of each cell in the "Meaning" column.

  <p class=note>Some Level 4 selectors (noted above as "3-UI") were
   introduced in <a href="#CSS3UI"
   rel=biblioentry>[CSS3UI]<!--{{CSS3UI}}--></a>.

  <h2 id=syntax><span class=secno>3. </span> Selector Syntax and Structure</h2>

  <h3 id=structure><span class=secno>3.1. </span> Structure and Terminology</h3>

  <p>The term <dfn id=selector>selector</dfn> can refer to a <i>simple
   selector</i>, <a href="#compound"><i>compound selector</i></a>, <a
   href="#complex"><i>complex selector</i></a>, or <a
   href="#selector-list"><i>selector list</i></a>.

  <p>A <dfn id=complex>complex selector</dfn> is a chain of one or more <a
   href="#compound">compound selectors</a> separated by <a
   href="#combinators">combinators</a>.

  <p>A <dfn id=compound>compound selector</dfn> is a chain of <a
   href="#simple">simple selectors</a> that are not separated by a <a
   href="#combinators">combinator</a>. It always begins with a <a
   href="#type-selectors">type selector</a> or a (possibly implied) <a
   href="#universal-selector">universal selector</a>. No other type selector
   or universal selector is allowed in the sequence.

  <p>A <dfn id=simple><a href="#simple">simple selector</a></dfn> is either a
   <a href="#type-selectors">type selector</a>, <a
   href="#universal-selector">universal selector</a>, <a
   href="#attribute-selectors">attribute selector</a>, <a
   href="#class-html">class selector</a>, <a href="#id-selectors">ID
   selector</a>, or <a href="#pseudo-classes">pseudo-class</a>.

  <p><dfn id=combinator>Combinators</dfn> are punctuation that represent a
   particular kind of relationship between the compound selectors on either
   side. Combinators in Selectors level 4 include: whitespace,
   &quot;greater-than sign&quot; (U+003E, <code>&gt;</code>), &quot;plus
   sign&quot; (U+002B, <code>+</code>) and &quot;tilde&quot; (U+007E,
   <code>~</code>). <a href="#whitespace">White space</a> may appear between
   a combinator and the simple selectors around it.

  <p>An empty selector, containing no compound selector, is an <a
   href="#invalid">invalid selector</a>.

  <h3 id=subject><span class=secno>3.2. </span> Determining the Subject of a
   Selector</h3>

  <p>The elements of a document tree that are represented by a selector are
   the <dfn id=subjects>subjects</dfn> of the selector.

  <p>By default, the subjects of a selector are the elements represented by
   the last compound selector in the selector. Thus a selector consisting of
   a single compound selector represents any element satisfying its
   requirements. Prepending another compound selector and a combinator to a
   sequence imposes additional matching constraints, so the subjects of the
   selector are always a subset of the elements represented by the last
   compound selector.

  <p>The subject of the selector can be explicitly identified by prepending a
   dollar sign ($) to one of the compound selectors in a selector. Although
   the element structure that the selector represents is the same with or
   without the dollar sign, indicating the subject in this way can change
   which compound selector represents the subject in that structure.

  <div class=example>
   <p>For example, the following selector represents a list item
    <code>LI</code> unique child of an ordered list <code>OL</code>:

   <pre>OL &gt; LI:only-child</pre>

   <p>However the following one represents an ordered list <code>OL</code>
    having a unique child, that child being a <code>LI</code>:

   <pre>$OL &gt; LI:only-child</pre>

   <p>The structures represented by these two selectors are the same, but the
    subjects of the selectors are not.
  </div>

  <h3 id=pseudo-classes><span class=secno>3.3. </span> Pseudo-classes</h3>

  <p>The pseudo-class concept is introduced to permit selection based on
   information that lies outside of the document tree or that cannot be
   expressed using the other simple selectors.

  <p>A pseudo-class always consists of a &quot;colon&quot; (<code>:</code>)
   followed by the name of the pseudo-class and, for functional
   pseudo-classes, by a value between parentheses. White space is optionally
   allowed between the parentheses and the argument, but not between the
   pseudo-class name and the parentheses.

  <p>Pseudo-classes are allowed in all compound selectors contained in a
   selector. Pseudo-classes are allowed anywhere in a compound selector after
   the leading type selector or (possibly omitted) universal selector.
   Pseudo-class names are case-insensitive. Some pseudo-classes are mutually
   exclusive (such that a compound selector containing them, while valid,
   will never match anything), while others can apply simultaneously to the
   same element. Pseudo-classes may be dynamic, in the sense that an element
   can acquire or lose a pseudo-class while a user interacts with the
   document.

  <p>Dynamic pseudo-classes classify elements on characteristics other than
   their name, attributes, or content, in principle characteristics that
   cannot be deduced from the document tree.

  <p>Dynamic pseudo-classes do not appear in the document source or document
   tree.

  <h3 id=pseudo-elements><span class=secno>3.4. </span>Pseudo-elements</h3>

  <p>Pseudo-elements create abstractions about the document tree beyond those
   specified by the document language. For instance, document languages do
   not offer mechanisms to access the first letter or first line of an
   element's content. Pseudo-elements allow authors to refer to this
   otherwise inaccessible information. Pseudo-elements may also provide
   authors a way to refer to content that does not exist in the source
   document (e.g., the <code>::before</code> and <code>::after</code>
   pseudo-elements give access to generated content in CSS <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{CSS21}}--></a>).

  <p>A pseudo-element is made of two colons (<code>::</code>) followed by the
   name of the pseudo-element.

  <p>This <code>::</code> notation was chosen in order to establish a
   discrimination between pseudo-classes (which subclass existing elements)
   and pseudo-elements (which are elements not represented in the document
   tree). However, for compatibility with existing style sheets, user agents
   must also accept the previous one-colon notation for pseudo-elements
   introduced in CSS levels 1 and 2 (namely, <code>:first-line</code>,
   <code>:first-letter</code>, <code>:before</code> and <code>:after</code>).
   This compatibility notation is not allowed any other pseudo-elements.

  <p>Only one pseudo-element may appear per selector, and only if the subject
   of the selector is the last compound selector in the selector. If present
   the pseudo-element must appear after the compound selector that represents
   the <a href="#subject">subjects</a> of the selector.

  <p class=note>A future version of this specification may allow multiple
   pseudo-elements per selector.

  <p>Syntactically, a pseudo-element may be followed by any combination of
   the <a href="#useraction-pseudos">user action pseudo-classes</a>. Whether
   these pseudo-classes can match on the pseudo-element depends on the
   pseudo-class and pseudo-element's definition: unless otherwise-specified,
   none of these pseudo-classes will match on the pseudo-element.

  <div class=example>
   <p>For example, the <code>:hover</code> pseudo-class specifies that it can
    apply to any pseudo-element, i.e. <code>::first-line:hover</code> will
    match when the first line is hovered. However, since neither
    <code>:focus</code> nor <code>::first-line</code> define that
    <code>:focus</code> can apply to <code>::first-line</code>, the selector
    <code>::first-line:focus</code> will never match anything.
  </div>

  <h3 id=case-sensitive><span class=secno>3.5. </span> Characters and case
   sensitivity</h3>

  <p>All Selectors syntax is case-insensitive within the ASCII range (i.e.
   [a-z] and [A-Z] are equivalent), except for parts that are not under the
   control of Selectors. The case sensitivity of document language element
   names, attribute names, and attribute values in selectors depends on the
   document language. For example, in HTML, element names are
   case-insensitive, but in XML, they are case-sensitive. Case sensitivity of
   namespace prefixes is defined in <a href="#CSS3NAMESPACE"
   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>.

  <p><dfn id=whitespace>White space</dfn> in Selectors consists of the
   characters SPACE (U+0020), TAB (U+0009), LINE FEED (U+000A), CARRIAGE
   RETURN (U+000D), and FORM FEED (U+000C) can occur in whitespace. Other
   space-like characters, such as EM SPACE (U+2003) and IDEOGRAPHIC SPACE
   (U+3000), are never part of white space.

  <p>Characters in Selectors can be escaped with a backslash according to the
   same <a href="http://www.w3.org/TR/CSS21/syndata.html#characters">escaping
   rules</a> as CSS. <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.

  <h3 id=namespaces><span class=secno>3.6. </span> Namespaces</h3>

  <p>Certain selectors support namespace prefixes. The mechanism by which
   namespace prefixes are <dfn id=nsdecl>declared</dfn> should be specified
   by the language that uses Selectors. If the language does not specify a
   namespace prefix declaration mechanism, then no prefixes are declared. In
   CSS, namespace prefixes are declared with the <a
   href="http://www.w3.org/TR/css3-namespace/#declaration"><code>@namespace</code></a>
   rule. <a href="#CSS3NAMESPACE"
   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>

  <h3 id=invalid><span class=secno>3.7. </span> Invalid Selectors and Error
   Handling</h3>

  <p>Invalidity is caused by a parsing error, e.g. an unrecognized token or a
   token which is not allowed at the current parsing point.

  <p>User agents must observe the rules for handling parsing errors:

  <ul>
   <li>a simple selector containing an <a href="#namespaces">undeclared
    namespace prefix</a> is invalid

   <li>a selector containing an invalid simple selector, an invalid
    combinator or an invalid token is invalid.

   <li>a selector list containing an invalid selector is invalid.
  </ul>

  <p>An invalid selector represents nothing.

  <p class=issue>It's been <a
   href="http://lists.w3.org/Archives/Public/www-style/2010Nov/0203.html">requested</a>
   that the last rule be dropped in favor of Media Queries-style
   error-handling.

  <h2 id=logical-combination><span class=secno>4. </span> Logical
   Combinations</h2>

  <h3 id=grouping><span class=secno>4.1. </span> Selector Lists</h3>

  <p>A comma-separated list of selectors represents the union of all elements
   selected by each of the individual selectors in the <dfn
   id=selector-list>selector list</dfn>. (A comma is U+002C.) For example, in
   CSS when several selectors share the same declarations, they may be
   grouped into a comma-separated list. White space may appear before and/or
   after the comma.

  <div class=example>
   <p>CSS example:</p>

   <p>In this example, we condense three rules with identical declarations
    into one. Thus,</p>

   <pre>h1 { font-family: sans-serif }
  h2 { font-family: sans-serif }
  h3 { font-family: sans-serif }</pre>

   <p>is equivalent to:</p>

   <pre>h1, h2, h3 { font-family: sans-serif }</pre>
  </div>

  <p><strong>Warning</strong>: the equivalence is true in this example
   because all the selectors are valid selectors. If just one of these
   selectors were invalid, the entire group of selectors would be invalid.
   This would invalidate the rule for all three heading elements, whereas in
   the former case only one of the three individual heading rules would be
   invalidated.

  <div class=example>
   <p>Invalid CSS example:</p>

   <pre>h1 { font-family: sans-serif }
  h2..foo { font-family: sans-serif }
  h3 { font-family: sans-serif }</pre>

   <p>is not equivalent to:</p>

   <pre>h1, h2..foo, h3 { font-family: sans-serif }</pre>

   <p>because the above selector (<code>h1, h2..foo, h3</code>) is entirely
    invalid and the entire style rule is dropped. (When the selectors are not
    grouped, only the rule for <code>h2..foo</code> is dropped.)</p>
  </div>

  <h3 id=matches><span class=secno>4.2. </span> The Matches-Any Pseudo-class:
   &lsquo;<code class=css>:matches()</code>&rsquo;</h3>

  <p>The matches-any pseudo-class, <code>:matches(<var>X</var>)</code>, is a
   functional notation taking a <a href="#grouping">selector list</a> as its
   argument. It represents an element that is represented by its argument.

  <p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
   are allowed within <code>:matches()</code>: <a
   href="#combinator">combinators</a> are not allowed. Additionally,
   <code>:matches()</code> may not be nested within itself or within
   <code>:not()</code>: <code>:matches(:matches(...))</code> and
   <code>:not(:matches(...))</code> are invalid.

  <p>Pseudo-elements cannot be represented by the matches-any pseudo-class;
   they are not valid within <code>:matches()</code>.

  <p>Default namespace declarations do not affect the subject of any selector
   within a matches-any pseudo-class unless the argument is an explicit
   universal selector or a type selector.

  <div class=example>
   <p>For example, following selector matches any element that is being
    hovered or focused, regardless of its namespace. In particular, it is not
    limited to only matching elements in the default namespace that are being
    hovered or focused.</p>

   <pre>*|*:matches(:hover, :focus)</pre>

   <p>The following selector, however, represents only hovered or focused
    elements that are in the default namespace, because it uses an explicit
    universal selector within the <code>:matches()</code> notation:</p>

   <pre>*|*:matches(*:hover, *:focus)</pre>
  </div>

  <h3 id=negation><span class=secno>4.3. </span> The Negation Pseudo-class:
   &lsquo;<code class=css>:not()</code>&rsquo;</h3>

  <p>The negation pseudo-class, <code>:not(<var>X</var>)</code>, is a
   functional notation taking a <a href="#grouping">selector list</a> as an
   argument. It represents an element that is not represented by its
   argument.

  <p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
   are allowed within <code>:matches()</code>: <a
   href="#combinator">combinators</a> are not allowed. Additionally,
   negations may not be nested within itself or within
   <code>:matches()</code>: <code>:not(:not(...))</code> and
   <code>:matches(:not(...))</code> are invalid.

  <p>Pseudo-elements cannot be represented by the negation pseudo-class; they
   are not valid within <code>:not()</code>.

  <div class=example>
   <p>For example, the following selector matches all <code>button</code>
    elements in an HTML document that are not disabled.</p>

   <pre>button:not([DISABLED])</pre>

   <p>The following selector represents all but <code>FOO</code> elements.</p>

   <pre>*:not(FOO)</pre>

   <p>The following compound selector represents all HTML elements except
    links.</p>

   <pre>html|*:not(:link):not(:visited)</pre>
  </div>

  <p>Default namespace declarations do not affect the subject of any selector
   within a negation pseudo-class unless the argument is an explicit
   universal selector or a type selector. (See <a
   href="#matches"><code>:matches()</code></a> for examples.

  <p class=note><strong>Note</strong>: the :not() pseudo allows useless
   selectors to be written. For instance <code>:not(*|*)</code>, which
   represents no element at all, or <code>foo:not(bar)</code>, which is
   equivalent to <code>foo</code> but with a higher specificity.

  <h2 id=elemental-selectors><span class=secno>5. </span> Elemental selectors</h2>

  <h3 id=type-selectors><span class=secno>5.1. </span> Type selector</h3>

  <p>A <dfn id=type-selector>type selector</dfn> is the name of a document
   language element type written using the syntax of <a
   href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
   names</a> <a href="#CSS3NAMESPACE"
   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>. A type
   selector represents an instance of the element type in the document tree.

  <div class=example>
   <p>Example:</p>

   <p>The following selector represents an <code>h1</code> element in the
    document tree:</p>

   <pre>h1</pre>
  </div>

  <h4 id=typenmsp><span class=secno>5.1.1. </span> Type selectors and
   namespaces</h4>

  <p>Type selectors allow an optional namespace component: a namespace prefix
   that has been previously <a href="#nsdecl">declared</a> may be prepended
   to the element name separated by the namespace separator &quot;vertical
   bar&quot; (U+007C, <code>|</code>). (See, e.g., <a href="#XML-NAMES"
   rel=biblioentry>[XML-NAMES]<!--{{XML-NAMES}}--></a> for the use of
   namespaces in XML.)

  <p>The namespace component may be left empty (no prefix before the
   namespace separator) to indicate that the selector is only to represent
   elements with no namespace.

  <p>An asterisk may be used for the namespace prefix, indicating that the
   selector represents elements in any namespace (including elements with no
   namespace).

  <p>Element type selectors that have no namespace component (no namespace
   separator) represent elements without regard to the element's namespace
   (equivalent to "<code>*|</code>") unless a default namespace has been <a
   href="#nsdecl">declared</a> for namespaced selectors (e.g. in CSS, in the
   style sheet). If a default namespace has been declared, such selectors
   will represent only elements in the default namespace.

  <p>A type selector containing a namespace prefix that has not been
   previously <a href="#nsdecl">declared</a> for namespaced selectors is an
   <a href="#conformance">invalid</a> selector.

  <p>In a namespace-aware client, the name part of element type selectors
   (the part after the namespace separator, if it is present) will only match
   against the <a
   href="http://www.w3.org/TR/REC-xml-names/#NT-LocalPart">local part</a> of
   the element's <a
   href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">qualified
   name</a>.

  <p>In summary:

  <dl>
   <dt><code>ns|E</code>

   <dd>elements with name E in namespace ns

   <dt><code>*|E</code>

   <dd>elements with name E in any namespace, including those without a
    namespace

   <dt><code>|E</code>

   <dd>elements with name E without a namespace

   <dt><code>E</code>

   <dd>if no default namespace has been <a href="#nsdecl">declared</a> for
    selectors, this is equivalent to *|E. Otherwise it is equivalent to ns|E
    where ns is the default namespace.
  </dl>

  <div class=example>
   <p>CSS examples:</p>

   <pre>@namespace foo url(http://www.example.com);
   foo|h1 { color: blue }  /* first rule */
   foo|* { color: yellow } /* second rule */
   |h1 { color: red }      /* ...*/
   *|h1 { color: green }
   h1 { color: green }</pre>

   <p>The first rule (not counting the <code>@namespace</code> at-rule) will
    match only <code>h1</code> elements in the "http://www.example.com"
    namespace.</p>

   <p>The second rule will match all elements in the "http://www.example.com"
    namespace.</p>

   <p>The third rule will match only <code>h1</code> elements with no
    namespace.</p>

   <p>The fourth rule will match <code>h1</code> elements in any namespace
    (including those without any namespace).</p>

   <p>The last rule is equivalent to the fourth rule because no default
    namespace has been defined.</p>
  </div>

  <h3 id=universal-selector><span class=secno>5.2. </span> Universal selector
   </h3>

  <p>The <dfn id=universal-selector0>universal selector</dfn>, written as a
   <a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
   name</a> <a href="#CSS3NAMESPACE"
   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a> with an
   asterisk (<code>*</code> U+002A) as the local name, represents the
   qualified name of any element type. It represents any single element in
   the document tree in any namespace (including those without a namespace)
   if no default namespace has been specified for selectors. If a default
   namespace has been specified, see <a href="#univnmsp">Universal selector
   and Namespaces</a> below.

  <p>If a universal selector represented by <code>*</code> (i.e. without a
   namespace prefix) is not the only component of a <a
   href="#compound">compound selector</a> or is immediately followed by a <a
   href="#pseudo-elements">pseudo-element</a>, then the <code>*</code> may be
   omitted and the universal selector's presence implied.

  <div class=example>
   <p>Examples:</p>

   <ul>
    <li><code>*[hreflang|=en]</code> and <code>[hreflang|=en]</code> are
     equivalent,

    <li><code>*.warning</code> and <code>.warning</code> are equivalent,

    <li><code>*#myid</code> and <code>#myid</code> are equivalent.
   </ul>
  </div>

  <p class=note><strong>Note:</strong> it is recommended that the
   <code>*</code> not be omitted, because it decreases the potential
   confusion between, for example, <code style="white-space: nowrap">div
   :first-child</code> and <code style="white-space:
   nowrap">div:first-child</code>. Here, <code style="white-space:
   nowrap">div *:first-child</code> is more readable.

  <h4 id=univnmsp><span class=secno>5.2.1. </span> Universal selector and
   namespaces</h4>

  <p>The universal selector allows an optional namespace component. It is
   used as follows:

  <dl>
   <dt><code>ns|*</code>

   <dd>all elements in namespace ns

   <dt><code>*|*</code>

   <dd>all elements

   <dt><code>|*</code>

   <dd>all elements without a namespace

   <dt><code>*</code>

   <dd>if no default namespace has been specified, this is equivalent to *|*.
    Otherwise it is equivalent to ns|* where ns is the default namespace.
  </dl>

  <p>A universal selector containing a namespace prefix that has not been
   previously <a href="#nsdecl">declared</a> is an <a
   href="#conformance">invalid</a> selector.

  <h2 id=attribute-selectors><span class=secno>6. </span> Attribute selectors</h2>

  <p>Selectors allow the representation of an element's attributes. When a
   selector is used as an expression to match against an element, attribute
   selectors must be considered to match an element if that element has an
   attribute that matches the attribute represented by the attribute
   selector.

  <h3 id=attribute-representation><span class=secno>6.1. </span> Attribute
   presence and value selectors</h3>

  <p>CSS2 introduced four attribute selectors:

  <dl>
   <dt><code>[att]</code>

   <dd>Represents an element with the <code>att</code> attribute, whatever
    the value of the attribute.

   <dt><code>[att=val]</code>

   <dd>Represents an element with the <code>att</code> attribute whose value
    is exactly "val".

   <dt><code>[att~=val]</code>

   <dd>Represents an element with the <code>att</code> attribute whose value
    is a <a href="#whitespace">whitespace</a>-separated list of words, one of
    which is exactly "val". If "val" contains whitespace, it will never
    represent anything (since the words are <em>separated</em> by spaces).
    Also if "val" is the empty string, it will never represent anything.

   <dt><code>[att|=val]</code>

   <dd>Represents an element with the <code>att</code> attribute, its value
    either being exactly "val" or beginning with "val" immediately followed
    by "-" (U+002D). This is primarily intended to allow language subcode
    matches (e.g., the <code>hreflang</code> attribute on the <code>a</code>
    element in HTML) as described in BCP 47 (<a href="#BCP47"
    rel=biblioentry>[BCP47]<!--{{BCP47}}--></a>) or its successor. For
    <code>lang</code> (or <code>xml:lang</code>) language subcode matching,
    please see <a href="#lang-pseudo">the <code>:lang</code>
    pseudo-class</a>.
  </dl>

  <p>Attribute values must be CSS <a
   href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
   or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>.
   <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

  <div class=example>
   <p>Examples:</p>

   <p>The following attribute selector represents an <code>h1</code> element
    that carries the <code>title</code> attribute, whatever its value:</p>

   <pre>h1[title]</pre>

   <p>In the following example, the selector represents a <code>span</code>
    element whose <code>class</code> attribute has exactly the value
    "example":</p>

   <pre>span[class="example"]</pre>

   <p>Multiple attribute selectors can be used to represent several
    attributes of an element, or several conditions on the same attribute.
    Here, the selector represents a <code>span</code> element whose
    <code>hello</code> attribute has exactly the value "Cleveland" and whose
    <code>goodbye</code> attribute has exactly the value "Columbus":</p>

   <pre>span[hello="Cleveland"][goodbye="Columbus"]</pre>

   <p>The following CSS rules illustrate the differences between "=" and
    "~=". The first selector would match, for example, an <code>a</code>
    element with the value "copyright copyleft copyeditor" on a
    <code>rel</code> attribute. The second selector would only match an
    <code>a</code> element with an <code>href</code> attribute having the
    exact value "http://www.w3.org/".</p>

   <pre>a[rel~="copyright"] { ... }
  a[href="http://www.w3.org/"] { ... }</pre>

   <p>The following selector represents an <code>a</code> element whose
    <code>hreflang</code> attribute is exactly "fr".</p>

   <pre>a[hreflang=fr]</pre>

   <p>The following selector represents an <code>a</code> element for which
    the value of the <code>hreflang</code> attribute begins with "en",
    including "en", "en-US", and "en-scouse":</p>

   <pre>a[hreflang|="en"]</pre>

   <p>The following selectors represent a <code>DIALOGUE</code> element
    whenever it has one of two different values for an attribute
    <code>character</code>:</p>

   <pre>DIALOGUE[character=romeo]
  DIALOGUE[character=juliet]</pre>
  </div>

  <h3 id=attribute-substrings><span class=secno>6.2. </span> Substring
   matching attribute selectors</h3>

  <p>Three additional attribute selectors are provided for matching
   substrings in the value of an attribute:

  <dl>
   <dt><code>[att^=val]</code>

   <dd>Represents an element with the <code>att</code> attribute whose value
    begins with the prefix "val". If "val" is the empty string then the
    selector does not represent anything.

   <dt><code>[att$=val]</code>

   <dd>Represents an element with the <code>att</code> attribute whose value
    ends with the suffix "val". If "val" is the empty string then the
    selector does not represent anything.

   <dt><code>[att*=val]</code>

   <dd>Represents an element with the <code>att</code> attribute whose value
    contains at least one instance of the substring "val". If "val" is the
    empty string then the selector does not represent anything.
  </dl>

  <p>Attribute values must be CSS <a
   href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
   or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>.
   <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

  <div class=example>
   <p>Examples:</p>

   <p>The following selector represents an HTML <code>object</code>,
    referencing an image:</p>

   <pre>object[type^="image/"]</pre>

   <p>The following selector represents an HTML anchor <code>a</code> with an
    <code>href</code> attribute whose value ends with ".html".</p>

   <pre>a[href$=".html"]</pre>

   <p>The following selector represents an HTML paragraph with a
    <code>title</code> attribute whose value contains the substring "hello"</p>

   <pre>p[title*="hello"]</pre>
  </div>

  <h3 id=attribute-case><span class=secno>6.3. </span> Case-sensitivity</h3>

  <p>By default case-sensitivity of attribute names and values in selectors
   depends on the document language. To match attribute values
   case-insensitively regardless of document language rules, the attribute
   selector may include the identifier <code>i</code> immediately inside the
   closing bracket (<code>]</code>). When this flag is present, UAs must
   match the attribute's value case-insensitively within the ASCII range.

  <div class=example>
   <p>The following rule will style the <code>frame</code> attribute when it
    has a value of <code>hsides</code>, whether that value is represented as
    <code>hsides</code>, <code>HSIDES</code>, <code>hSides</code>, etc. even
    in an XML environment where attribute values are case-sensitive.

   <pre>
<!-- -->[frame=hsides i] { border-style: solid none; }
    </pre>
  </div>

  <h3 id=attrnmsp><span class=secno>6.4. </span> Attribute selectors and
   namespaces</h3>

  <p>The attribute name in an attribute selector is given as a <a
   href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
   name</a>: a namespace prefix that has been previously <a
   href="#nsdecl">declared</a> may be prepended to the attribute name
   separated by the namespace separator &quot;vertical bar&quot;
   (<code>|</code>). In keeping with the Namespaces in the XML
   recommendation, default namespaces do not apply to attributes, therefore
   attribute selectors without a namespace component apply only to attributes
   that have no namespace (equivalent to "<code>|attr</code>"). An asterisk
   may be used for the namespace prefix indicating that the selector is to
   match all attribute names without regard to the attribute's namespace.

  <p>An attribute selector with an attribute name containing a namespace
   prefix that has not been previously <a href="#nsdecl">declared</a> is an
   <a href="#conformance">invalid</a> selector.

  <div class=example>
   <p>CSS examples:</p>

   <pre>@namespace foo "http://www.example.com";
  [foo|att=val] { color: blue }
  [*|att] { color: yellow }
  [|att] { color: green }
  [att] { color: green }</pre>

   <p>The first rule will match only elements with the attribute
    <code>att</code> in the "http://www.example.com" namespace with the value
    "val".</p>

   <p>The second rule will match only elements with the attribute
    <code>att</code> regardless of the namespace of the attribute (including
    no namespace).</p>

   <p>The last two rules are equivalent and will match only elements with the
    attribute <code>att</code> where the attribute is not in a namespace.</p>
  </div>

  <h3 id=def-values><span class=secno>6.5. </span> Default attribute values
   in DTDs</h3>

  <p>Attribute selectors represent attribute values in the document tree. How
   that document tree is constructed is outside the scope of Selectors. In
   some document formats default attribute values can be defined in a DTD or
   elsewhere, but these can only be selected by attribute selectors if they
   appear in the document tree. Selectors should be designed so that they
   work whether or not the default values are included in the document tree.

  <p>For example, a XML UA may, but is <em>not</em> required to read an
   "external subset" of the DTD but <em>is</em> required to look for default
   attribute values in the document's "internal subset." (See, e.g., <a
   href="#XML10" rel=biblioentry>[XML10]<!--{{XML10}}--></a> for definitions
   of these subsets.) Depending on the UA, a default attribute value defined
   in the external subset of the DTD might or might not appear in the
   document tree.

  <p>A UA that recognizes an XML namespace may, but is not required to use
   its knowledge of that namespace to treat default attribute values as if
   they were present in the document. (For example, an XHTML UA is not
   required to use its built-in knowledge of the XHTML DTD. See, e.g., <a
   href="#XML-NAMES" rel=biblioentry>[XML-NAMES]<!--{{XML-NAMES}}--></a> for
   details on namespaces in XML 1.0.)

  <p class=note><strong>Note:</strong> Typically, implementations choose to
   ignore external subsets. This corresponds to the behaviour of
   non-validating processors as defined by the XML specification.

  <div class=example>
   <p>Example:</p>

   <p>Consider an element <code>EXAMPLE</code> with an attribute
    <code>radix</code> that has a default value of <code>"decimal"</code>.
    The DTD fragment might be</p>

   <pre
    class=dtd-example>&lt;!ATTLIST EXAMPLE radix (decimal,octal) "decimal"></pre>

   <p>If the style sheet contains the rules</p>

   <pre>EXAMPLE[radix=decimal] { /*... default property settings ...*/ }
  EXAMPLE[radix=octal]   { /*... other settings...*/ }</pre>

   <p>the first rule might not match elements whose <code>radix</code>
    attribute is set by default, i.e. not set explicitly. To catch all cases,
    the attribute selector for the default value must be dropped:</p>

   <pre>EXAMPLE                { /*... default property settings ...*/ }
  EXAMPLE[radix=octal]   { /*... other settings...*/ }</pre>

   <p>Here, because the selector <code>EXAMPLE[radix=octal]</code> is more
    specific than the type selector alone, the style declarations in the
    second rule will override those in the first for elements that have a
    <code>radix</code> attribute value of <code>"octal"</code>. Care has to
    be taken that all property declarations that are to apply only to the
    default case are overridden in the non-default cases' style rules.</p>
  </div>

  <h3 id=class-html><span class=secno>6.6. </span> Class selectors</h3>

  <p>The class selector is given as a full stop (. U+002E) immediately
   followed by an identifier. It represents an element belonging to the class
   identified by the identifier, as defined by the document language. For
   example, in <a href="#HTML5" rel=biblioentry>[HTML5]<!--{{HTML5}}--></a>,
   <a href="#SVG11" rel=biblioentry>[SVG11]<!--{{SVG11}}--></a>, and <a
   href="#MATHML" rel=biblioentry>[MATHML]<!--{{MATHML}}--></a> membership in
   a class is given by the <code>class</code> attribute: in these languages
   it is equivalent to the <code>~=</code> notation applied to the local
   <code>class</code> attribute (i.e.
   <code>[class~=<var>identifier</var>]</code>), except that it has a higher
   <a href="#specificity">specificity</a>.

  <div class=example>
   <p>CSS examples:</p>

   <p>We can assign style information to all elements with
    <code>class~="pastoral"</code> as follows:</p>

   <pre>*.pastoral { color: green }  /* all elements with class~=pastoral */</pre>

   <p>or just</p>

   <pre>.pastoral { color: green }  /* all elements with class~=pastoral */</pre>

   <p>The following assigns style only to H1 elements with
    <code>class~="pastoral"</code>:</p>

   <pre>H1.pastoral { color: green }  /* H1 elements with class~=pastoral */</pre>

   <p>Given these rules, the first <code>H1</code> instance below would not
    have green text, while the second would:</p>

   <pre>&lt;H1&gt;Not green&lt;/H1&gt;
  &lt;H1 class="pastoral"&gt;Very green&lt;/H1&gt;</pre>

   <p>The following rule matches any <code>P</code> element whose
    <code>class</code> attribute has been assigned a list of <a
    href="#whitespace">whitespace</a>-separated values that includes both
    <code>pastoral</code> and <code>marine</code>:</p>

   <pre>p.pastoral.marine { color: green }</pre>

   <p>This rule matches when <code>class="pastoral blue aqua marine"</code>
    but does not match for <code>class="pastoral blue"</code>.</p>
  </div>

  <p class=note><strong>Note:</strong> Because CSS gives considerable power
   to the "class" attribute, authors could conceivably design their own
   "document language" based on elements with almost no associated
   presentation (such as <code>DIV</code> and <code>SPAN</code> in HTML) and
   assigning style information through the "class" attribute. Authors should
   avoid this practice since the structural elements of a document language
   often have recognized and accepted meanings and author-defined classes may
   not.

  <p class=note><strong>Note:</strong> If an element has multiple class
   attributes, their values must be concatenated with spaces between the
   values before searching for the class. As of this time the working group
   is not aware of any manner in which this situation can be reached,
   however, so this behavior is explicitly non-normative in this
   specification.

  <h3 id=id-selectors><span class=secno>6.7. </span> ID selectors</h3>

  <p>Document languages may contain attributes that are declared to be of
   type ID. What makes attributes of type ID special is that no two such
   attributes can have the same value in a conformant document, regardless of
   the type of the elements that carry them; whatever the document language,
   an ID typed attribute can be used to uniquely identify its element. In
   HTML all ID attributes are named "id"; XML applications may name ID
   attributes differently, but the same restriction applies.

  <p>An ID-typed attribute of a document language allows authors to assign an
   identifier to one element instance in the document tree. An ID selector
   contains a &quot;number sign&quot; (U+0023, <code>#</code>) immediately
   followed by the ID value, which must be an CSS <a
   href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>.
   An ID selector represents an element instance that has an identifier that
   matches the identifier in the ID selector.

  <p>Selectors does not specify how a UA knows the ID-typed attribute of an
   element. The UA may, e.g., read a document's DTD, have the information
   hard-coded or ask the user.

  <div class=example>
   <p>Examples:</p>

   <p>The following ID selector represents an <code>h1</code> element whose
    ID-typed attribute has the value "chapter1":</p>

   <pre>h1#chapter1</pre>

   <p>The following ID selector represents any element whose ID-typed
    attribute has the value "chapter1":</p>

   <pre>#chapter1</pre>

   <p>The following selector represents any element whose ID-typed attribute
    has the value "z98y".</p>

   <pre>*#z98y</pre>
  </div>

  <p class=note><strong>Note:</strong> In XML 1.0 <a href="#XML10"
   rel=biblioentry>[XML10]<!--{{XML10}}--></a>, the information about which
   attribute contains an element's IDs is contained in a DTD or a schema.
   When parsing XML, UAs do not always read the DTD, and thus may not know
   what the ID of an element is (though a UA may have namespace-specific
   knowledge that allows it to determine which attribute is the ID attribute
   for that namespace). If a style sheet author knows or suspects that a UA
   may not know what the ID of an element is, he should use normal attribute
   selectors instead: <code>[name=p371]</code> instead of <code>#p371</code>.

  <p>If an element has multiple ID attributes, all of them must be treated as
   IDs for that element for the purposes of the ID selector. Such a situation
   could be reached using mixtures of xml:id, DOM3 Core, XML DTDs, and
   namespace-specific knowledge.

  <h2 id=location><span class=secno>7. </span> Location Pseudo-classes</h2>

  <h3 id=any-link-pseudo><span class=secno>7.1. </span> The hyperlink
   pseudo-class: &lsquo;<code class=css>:any-link</code>&rsquo;</h3>

  <p>The <code>:any-link</code> pseudo-class represents an element that acts
   as the source anchor of a hyperlink.

  <p class=issue>Any better name suggestions for this pseudo?

  <p>

  <h3 id=link><span class=secno>7.2. </span> The link history pseudo-classes:
   &lsquo;<code class=css>:link</code>&rsquo; and &lsquo;<code
   class=css>:visited</code>&rsquo;</h3>

  <p>User agents commonly display unvisited links differently from previously
   visited ones. Selectors provides the pseudo-classes <code>:link</code> and
   <code>:visited</code> to distinguish them:

  <ul>
   <li>The <code>:link</code> pseudo-class applies to links that have not yet
    been visited.

   <li>The <code>:visited</code> pseudo-class applies once the link has been
    visited by the user.
  </ul>

  <p>After some amount of time, user agents may choose to return a visited
   link to the (unvisited) &lsquo;<code class=css>:link</code>&rsquo; state.

  <p>The two states are mutually exclusive.

  <div class=example>
   <p>Example:</p>

   <p>The following selector represents links carrying class
    <code>footnote</code> and already visited:</p>

   <pre>.footnote:visited</pre>
  </div>

  <p class=note><strong>Note:</strong> It is possible for style sheet authors
   to abuse the :link and :visited pseudo-classes to determine which sites a
   user has visited without the user's consent.

  <p>UAs may therefore treat all links as unvisited links, or implement other
   measures to preserve the user's privacy while rendering visited and
   unvisited links differently.

  <h3 id=local-pseudo><span class=secno>7.3. </span> The local link
   pseudo-class &lsquo;<code class=css>:local-link</code>&rsquo;</h3>

  <p>The <code>:local-link</code> pseudo-class allows authors to style links
   based on the users current location within a site and to differentiate
   site-internal versus site-external links. The <code>:local-link</code>
   pseudo-class represents an element that is the source anchor of a
   hyperlink whose target's absolute URI matches the element's own document
   URI. The fragment identifier of the document URI is stripped before
   matching against the link's URI; otherwise all portions of the URI are
   considered.

  <div class=example>
   <p>For example, the following rule prevents links targetting the current
    page from being underlined when they are part of the navigation list:

   <pre>nav :local-link { text-decoration: none; }</pre>
  </div>

  <p>The pseudo-class can also accept a non-negative integer as its sole
   argument, which, if the document's URI is a URL, indicates the number of
   path levels to match: an argument of zero represents a link element whose
   target is in the same domain as the document's URI, &lsquo;<code
   class=css>1</code>&rsquo; represents a link element whose target has the
   same domain and first path segment, &lsquo;<code class=css>2</code>&rsquo;
   represents a link element whose target has the same domain, first, and
   second path segments, etc. Path segments are portions of the URL's path
   that are separated by forward slashes (/). If a segment is missing from
   the document's URL, a pseudo-class requiring that segment to match does
   not match anything. Similarly if the document's URI is not a URL, the
   pseudo-class does not match anything. The scheme, username, password,
   port, query string, and fragment portions of the URL are not considered
   when matching against <code>:local-link(<var>n</var>)</code>.

  <p class=issue>Is there such a thing as IRL? Because we do want this to
   work for internationalized URLs, just not URNs.

  <div class=example>
   <p>So, given the links:

   <ol>
    <li><code>&lt;a href="http://www.example.com">Home&lt;/a></code>

    <li><code>&lt;a href="http://www.example.com/2011">2011&lt;/a></code>

    <li><code>&lt;a
     href="https://www.example.com/2011/03">March&lt;/a></code>

    <li><code>&lt;a
     href="http://www.example.com/2011/03/">March&lt;/a></code>

    <li><code>&lt;a href="http://example.com/2011/03">March&lt;/a></code>
   </ol>

   <p>and the styles:

   <ol>
    <li><code>a:local-link {...}</code>

    <li><code>a:local-link(0) {...}</code>

    <li><code>a:local-link(1) {...}</code>

    <li><code>a:local-link(2) {...}</code>

    <li><code>a:local-link(3) {...}</code>
   </ol>

   <p>If the document's URI is <code>http://www.example.com/2011/03/</code>:

   <ol>
    <li>Link 1 would receive Style 2

    <li>Link 2 would receive Styles 2 and 3

    <li>Link 3 would receive Styles 2, 3, and 4

    <li>Link 4 would receive Style 1

    <li>Link 5 would remain unstyled, and Style 5 would not be applied to
     anything.
   </ol>
  </div>

  <div class=example>
   <p>The following example styles all site-external links with a dashed
    underline.

   <pre>:not(:local-link(0)) { text-decoration-style: dashed; }</pre>
  </div>

  <h3 id=target-pseudo><span class=secno>7.4. </span> The target pseudo-class
   &lsquo;<code class=css>:target</code>&rsquo;</h3>

  <p>Some URIs refer to a location within a resource. This kind of URI ends
   with a &quot;number sign&quot; (#) followed by an anchor identifier
   (called the fragment identifier).

  <p>URIs with fragment identifiers link to a certain element within the
   document, known as the target element. For instance, here is a URI
   pointing to an anchor named <code>section_2</code> in an HTML document:

  <pre>http://example.com/html/top.html#section_2</pre>

  <p>A target element can be represented by the <code>:target</code>
   pseudo-class. If the document's URI has no fragment identifier, then the
   document has no target element.

  <div class=example>
   <p>Example:</p>

   <pre>p.note:target</pre>

   <p>This selector represents a <code>p</code> element of class
    <code>note</code> that is the target element of the referring URI.</p>
  </div>

  <div class=example>
   <p>CSS example:</p>

   <p>Here, the <code>:target</code> pseudo-class is used to make the target
    element red and place an image before it, if there is one:</p>

   <pre>*:target { color : red }
  *:target::before { content : url(target.png) }</pre>
  </div>

  <h3 id=scope-pseudo><span class=secno>7.5. </span> The contextual reference
   element pseudo-class &lsquo;<code class=css>:scope</code>&rsquo;</h3>

  <p>The <code>:scope</code> pseudo-class represents any element that is in
   the <a href="#contextual-reference-element-set"><i>contextual reference
   element set</i></a>. If no contextual reference element set is given,
   <code>:scope</code> is equivalent to <code>:root</code>.

  <p>The <dfn id=contextual-reference-element-set>contextual reference
   element set</dfn> is a (potentially empty) explicitly-specified set of
   elements, such as that specified by the <code>querySelector()</code> call
   in <a href="#SELECTORS-API2"
   rel=biblioentry>[SELECTORS-API2]<!--{{SELECTORS-API2}}--></a>.
   Specifications intending for this pseudo-class to match specific elements
   rather than the document's root element must define a contextual reference
   element set.

  <h2 id=useraction-pseudos><span class=secno>8. </span> User Action
   Pseudo-classes</h2>

  <p>Interactive user agents sometimes change the rendering in response to
   user actions. Selectors provides three pseudo-classes for the selection of
   an element the user is acting on.

  <p>These pseudo-classes are not mutually exclusive. An element may match
   several pseudo-classes at the same time.

  <div class=example>
   <p>Examples:</p>

   <pre>a:link    /* unvisited links */
  a:visited /* visited links */
  a:hover   /* user hovers */
  a:active  /* active links */</pre>

   <p>An example of combining dynamic pseudo-classes:</p>

   <pre>a:focus
  a:focus:hover</pre>

   <p>The last selector matches <code>a</code> elements that are in the
    pseudo-class :focus and in the pseudo-class :hover.</p>
  </div>

  <h3 id=hover-pseudo><span class=secno>8.1. </span> The pointer hover
   pseudo-class &lsquo;<code class=css>:hover</code>&rsquo;</h3>

  <p>The <code>:hover</code> pseudo-class applies while the user designates
   an element with a pointing device, but does not necessarily activate it.
   For example, a visual user agent could apply this pseudo-class when the
   cursor (mouse pointer) hovers over a box generated by the element. User
   agents not that do not support <a
   href="http://www.w3.org/TR/CSS21/media.html#interactive-media-group">interactive
   media</a> do not have to support this pseudo-class. Some conforming user
   agents that support <a
   href="http://www.w3.org/TR/CSS21/media.html#interactive-media-group">interactive
   media</a> may not be able to support this pseudo-class (e.g., a pen device
   that does not detect hovering).

  <p>The parent of an element that is <code>:hover</code> is also in that
   state.

  <p class=note><strong>Note:</strong> Since the &lsquo;<code
   class=css>:hover</code>&rsquo; state can apply to an element because its
   child is designated by a pointing device, then it is possible for
   &lsquo;<code class=css>:hover</code>&rsquo; to apply to an element that is
   not underneath the pointing device.

  <p>The <code>:hover</code> pseudo-class can apply to any pseudo-element.

  <h3 id=active-pseudo><span class=secno>8.2. </span> The activation
   pseudo-class &lsquo;<code class=css>:active</code>&rsquo;</h3>

  <p>The <code>:active</code> pseudo-class applies while an element is being
   activated by the user. For example, between the times the user presses the
   mouse button and releases it. On systems with more than one mouse button,
   <code>:active</code> applies only to the primary or primary activation
   button (typically the "left" mouse button), and any aliases thereof.

  <p>There may be document language or implementation specific limits on
   which elements can become <code>:active</code>.

  <p>Selectors doesn't define if the parent of an element that is
   &lsquo;<code class=css>:active</code>&rsquo; is also in that state.

  <p class=note><strong>Note:</strong> An element can be both &lsquo;<code
   class=css>:visited</code>&rsquo; and &lsquo;<code
   class=css>:active</code>&rsquo; (or &lsquo;<code
   class=css>:link</code>&rsquo; and &lsquo;<code
   class=css>:active</code>&rsquo;).

  <h3 id=focus-pseudo><span class=secno>8.3. </span> The input focus
   pseudo-class &lsquo;<code class=css>:focus</code>&rsquo;</h3>

  <p>The <code>:focus</code> pseudo-class applies while an element has the
   focus (accepts keyboard or mouse events, or other forms of input).

  <p>There may be document language or implementation specific limits on
   which elements can acquire <code>:focus</code>.

  <h2 id=time-pseudos><span class=secno>9. </span> Time-dimensional
   Pseudo-classes</h2>

  <p>These pseudo-classes classify elements with respect to the
   currently-displayed or active position in a time-dimensional canvas, such
   as during speech rendering of an HTML document.

  <h3 id=current-pseudo><span class=secno>9.1. </span> The current-element
   pseudo-class &lsquo;<code class=css>:current</code>&rsquo;</h3>

  <p>The <code>:current</code> pseudo-class represents the innermost element,
   or ancestor of an element, that is currently being displayed.

  <p>Its alternate form <code>:current()</code>, like
   <code>:matches()</code>, takes a list of compound selectors as its
   argument: it represents the <code>:current</code> element that matches the
   argument or, if that does not match, the innermost ancestor of the
   <code>:current</code> element that does. (If neither the
   <code>:current</code> element nor its ancestors match the argument, then
   the selector does not represent anything.)

  <div class=example>
   <p>For example, the following rule will highlight whichever paragraph or
    list item is being read aloud in a speech rendering of the document:

   <pre>
<!-- -->:current(p, li, dt, dd) {
<!-- -->  background: yellow;
<!-- -->}</pre>
  </div>

  <h3 id=past-pseudo><span class=secno>9.2. </span> The past-element
   pseudo-class &lsquo;<code class=css>:past</code>&rsquo;</h3>

  <p>The <code>:past</code> pseudo-class represents any element that is
   defined to occur entirely prior to a <code>:current</code> element. If a
   time-based order of elements is not defined by the document language, then
   this represents any element that is a (possibly indirect) previous sibling
   of a <code>:current</code> element.

  <h3 id=future-pseudo><span class=secno>9.3. </span> The future-element
   pseudo-class &lsquo;<code class=css>:future</code>&rsquo;</h3>

  <p>The <code>:future</code> pseudo-class represents any element that is
   defined to occur entirely after a <code>:current</code> element. If a
   time-based order of elements is not defined by the document language, then
   this represents any element that is a (possibly indirect) next sibling of
   a <code>:current</code> element.

  <h2 id=linguistic-pseudos><span class=secno>10. </span> Linguistic
   Pseudo-classes</h2>

  <h3 id=dir-pseudo><span class=secno>10.1. </span> The directionality
   pseudo-class &lsquo;<code class=css>:dir()</code>&rsquo;</h3>

  <p>The <code>:dir()</code> pseudo-class allows the author to write
   selectors that represent an element based on its directionality as
   determined by the document language. For example, in HTML <a
   href="#HTML401" rel=biblioentry>[HTML401]<!--{{HTML401}}--></a>, the
   directionality of an element is determined by the <code>dir</code>
   attribute. The <code>:dir()</code> pseudo-class does not select based on
   stylistic states&#8212;for example, the CSS &lsquo;<code
   class=property>direction</code>&rsquo; property does not affect whether it
   matches.

  <p>The pseudo-class <code>:dir(ltr)</code> represents an element that has a
   directionality of left-to-right (<code>ltr</code>). The pseudo-class
   <code>:dir(rtl)</code> represents an element that has a directionality of
   right-to-left (<code>rtl</code>). The argument to <code>:dir()</code> must
   be a single identifier, otherwise the selector is invlaid. White space is
   optionally allowed between the identifier and the parentheses. Values
   other than <code>ltr</code> and <code>rtl</code> are not invalid, but do
   not match anything. (If a future markup spec defines other
   directionalities, then Selectors may be extended to allow corresponding
   values.)

  <p>The difference between <code>:dir(C)</code> and <code>[dir=C]</code> is
   that <code>[dir=C]</code> only performs a comparison against a given
   attribute on the element, while the <code>:dir(C)</code> pseudo-class uses
   the UAs knowledge of the document's semantics to perform the comparison.
   For example, in HTML, the directionality of an element inherits so that a
   child without a <code>dir</code> attribute will have the same
   directionality as its closest ancestor with a valid <code>dir</code>
   attribute. As another example, <a
   href="http://www.w3.org/TR/html5/elements.html#the-directionality">in
   HTML5</a>, an element that matches <code>[dir=auto]</code> will match
   either <code>:dir(ltr)</code> or <code>:dir(rtl)</code> depending on the
   resolved directionality of the elements as determined by its contents. <a
   href="#HTML5" rel=biblioentry>[HTML5]<!--{{HTML5}}--></a>

  <h3 id=lang-pseudo><span class=secno>10.2. </span> The language
   pseudo-class &lsquo;<code class=css>:lang</code>&rsquo;</h3>

  <p>If the document language specifies how the human language of an element
   is determined, it is possible to write selectors that represent an element
   based on its language. For example, in HTML <a href="#HTML401"
   rel=biblioentry>[HTML401]<!--{{HTML401}}--></a>, the language is
   determined by a combination of the <code>lang</code> attribute and
   possibly information from the <code>meta</code> elements or the protocol
   (such as HTTP headers). XML uses an attribute called
   <code>xml:lang</code>, and there may be other document language-specific
   methods for determining the language.

  <p>The pseudo-class <code>:lang(C)</code> represents an element that is in
   language C. Whether an element is represented by a <code>:lang()</code>
   selector is based solely on the element's language value (normalized to
   BCP 47 syntax if necessary) being equal to the identifier C, or beginning
   with the identifier C immediately followed by "-" (U+002D). The matching
   of C against the element's language value is performed case-insensitively
   within the ASCII range. The identifier C does not have to be a valid
   language name.

  <p>C must be a valid CSS <a
   href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifier</a>
   <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> and must not
   be empty. (Otherwise, the selector is invalid.)

  <p class=note><strong>Note:</strong> It is recommended that documents and
   protocols indicate language using codes from BCP 47 <a href="#BCP47"
   rel=biblioentry>[BCP47]<!--{{BCP47}}--></a> or its successor, and by means
   of "xml:lang" attributes in the case of XML-based documents <a
   href="#XML10" rel=biblioentry>[XML10]<!--{{XML10}}--></a>. See <a
   href="http://www.w3.org/International/questions/qa-lang-2or3.html"> "FAQ:
   Two-letter or three-letter language codes."</a>

  <div class=example>
   <p>Examples:</p>

   <p>The two following selectors represent an HTML document that is in
    Belgian French or German. The two next selectors represent <code>q</code>
    quotations in an arbitrary element in Belgian French or German.</p>

   <pre>html:lang(fr-be)
  html:lang(de)
  :lang(fr-be) &gt; q
  :lang(de) &gt; q</pre>
  </div>

  <p>The difference between <code>:lang(C)</code> and the &lsquo;<code
   class=css>|=</code>&rsquo; operator is that the &lsquo;<code
   class=css>|=</code>&rsquo; operator only performs a comparison against a
   given attribute on the element, while the <code>:lang(C)</code>
   pseudo-class uses the UAs knowledge of the document's semantics to perform
   the comparison.

  <div class=example>
   <p>In this HTML example, only the BODY matches <code>[lang|=fr]</code>
    (because it has a LANG attribute) but both the BODY and the P match
    <code>:lang(fr)</code> (because both are in French). The P does not match
    the <code>[lang|=fr]</code> because it does not have a LANG attribute.</p>

   <pre>&lt;body lang=fr>
    &lt;p>Je suis fran&ccedil;ais.&lt;/p>
  &lt;/body></pre>
  </div>

  <h2 id=ui-states-pseudos><span class=secno>11. </span> The UI states
   pseudo-classes</h2>

  <h3 id=enableddisabled><span class=secno>11.1. </span> The &lsquo;<code
   class=css>:enabled</code>&rsquo; and &lsquo;<code
   class=css>:disabled</code>&rsquo; pseudo-classes</h3>

  <p>The <code>:enabled</code> pseudo-class represents user interface
   elements that are in an enabled state; such elements have a corresponding
   disabled state.

  <p>Conversely, the <code>:disabled</code> pseudo-class represents user
   interface elements that are in a disabled state; such elements have a
   corresponding enabled state.

  <p>What constitutes an enabled state, a disabled state, and a user
   interface element is language-dependent. In a typical document most
   elements will be neither <code>:enabled</code> nor <code>:disabled</code>.

  <p class=note><strong>Note:</strong> CSS properties that might affect a
   user’s ability to interact with a given user interface element do not
   affect whether it matches <code>:enabled</code> or <code>:disabled</code>;
   e.g., the <code>display</code> and <code>visibility</code> properties have
   no effect on the enabled/disabled state of an element.

  <h3 id=checked><span class=secno>11.2. </span> The selected-option
   pseudo-class &lsquo;<code class=css>:checked</code>&rsquo;</h3>

  <p>Radio and checkbox elements can be toggled by the user. Some menu items
   are "checked" when the user selects them. When such elements are toggled
   "on" the <code>:checked</code> pseudo-class applies. While the
   <code>:checked</code> pseudo-class is dynamic in nature, and can altered
   by user action, since it can also be based on the presence of semantic
   attributes in the document, it applies to all media. For example, the
   <code>:checked</code> pseudo-class initially applies to such elements that
   have the HTML4 <code>selected</code> and <code>checked</code> attributes
   as described in <a
   href="http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.2.1">Section
   17.2.1 of HTML4</a>, but of course the user can toggle "off" such elements
   in which case the <code>:checked</code> pseudo-class would no longer
   apply.

  <div class=example>
   <p>An unchecked checkbox can be selected by using the negation
    pseudo-class:

   <pre>:not(:checked)</pre>
  </div>

  <h3 id=indeterminate><span class=secno>11.3. </span> The
   indeterminate-value pseudo-class &lsquo;<code
   class=css>:indeterminate</code>&rsquo;</h3>

  <p>The <code>:indeterminate</code> pseudo-class applies to UI elements
   whose value is in an indeterminate state. For example, radio and checkbox
   elements can be toggled between checked and unchecked states, but are
   sometimes in an indeterminate state, neither checked nor unchecked.
   Similarly a progress meter can be in an indeterminate state when the
   percent completion is unknown.

  <p>Like the <code>:checked</code> pseudo-class, <code>:indeterminate</code>
   applies to all media. Components of a radio-group initialized with no
   pre-selected choice, for example, would be <code>:indeterminate</code>
   even in a static display.

  <h3 id=default-pseudo><span class=secno>11.4. </span> The default option
   pseudo-class &lsquo;<code class=css>:default</code>&rsquo;</h3>

  <p>The <dfn id=default-pseudo-class><code>:default</code>
   pseudo-class</dfn> applies to the one or more UI elements that are the
   default among a set of similar elements. Typically applies to context menu
   items, buttons and select lists/menus.

  <p>One example is the default submit button among a set of buttons. Another
   example is the default option from a popup menu. Multiple elements in a
   select-many group could have multiple <code>:default</code> elements, like
   a selection of pizza toppings for example.

  <h3 id=validity-pseudos><span class=secno>11.5. </span> The validity
   pseudo-classes &lsquo;<code class=css>:valid</code>&rsquo; and
   &lsquo;<code class=css>:invalid</code>&rsquo;</h3>

  <p>An element is <code id=valid-pseudo>:valid</code> or <code
   id=invalid-pseudo>:invalid</code> when its contents or value is,
   respectively, valid or invalid with respect to data validity semantics
   defined by the document language (e.g. <a href="#XFORMS10"
   rel=biblioentry>[XFORMS10]<!--{{XFORMS10}}--></a> or <a href="#HTML5"
   rel=biblioentry>[HTML5]<!--{{HTML5}}--></a>). An element which lacks data
   validity semantics is neither <code>:valid</code> nor
   <code>:invalid</code>. This is different from an element which otherwise
   has no constraints. Such an element would always be <code>:valid</code>.
   For example, a text input field with no constraints would always be
   <code>:valid</code>.

  <h3 id=range-pseudos><span class=secno>11.6. </span> The range
   pseudo-classes &lsquo;<code class=css>:in-range</code>&rsquo; and
   &lsquo;<code class=css>:out-of-range</code>&rsquo;</h3>

  <p>The <code id=in-range-psuedo>:in-range</code> and <code
   id=out-of-range-pseudo>:out-of-range</code> pseudo-classes apply only to
   elements that have range limitations. An element is <code>:in-range</code>
   or <code>:out-of-range</code> when the value that the element is bound to
   is in range or out of range with respect to its range limits as defined by
   the document language. An element that lacks data range limits or is not a
   form control is neither <code>:in-range</code> nor
   <code>:out-of-range</code>. E.g. a slider element with a value of 11
   presented as a slider control that only represents the values from 1-10 is
   :out-of-range. Another example is a menu element with a value of "E" that
   happens to be presented in a popup menu that only has choices "A", "B" and
   "C".

  <h3 id=opt-pseudos><span class=secno>11.7. </span> The optionality
   pseudo-classes &lsquo;<code class=css>:required</code>&rsquo; and
   &lsquo;<code class=css>:optional</code>&rsquo;</h3>

  <p>A form element is <code id=required-pseudo>:required</code> or <code
   id=optional-pseudo>:optional</code> if a value for it is, respectively,
   required or optional before the form it belongs to can be validly
   submitted. Elements that are not form elements are neither required nor
   optional.

  <h3 id=rw-pseudos><span class=secno>11.8. </span> The mutability
   pseudo-classes &lsquo;<code class=css>:read-only</code>&rsquo; and
   &lsquo;<code class=css>:read-write</code>&rsquo;</h3>

  <p>An element whose contents are not user-alterable is <code
   id=read-only-pseudo>:read-only</code>. However, elements whose contents
   are user-alterable (such as text input fields) are considered to be in a
   :read-write state. In typical documents, most elements are
   <code>:read-only</code>. However it may be possible, depending on the
   document language, for any element to become <code
   id=read-write-pseudo>:read-write</code>. For example, in HTML5 any element
   with the <code>contenteditable</code> attribute set to the true state is
   considered user-alterable. <a href="#HTML5"
   rel=biblioentry>[HTML5]<!--{{HTML5}}--></a>

  <h2 id=structural-pseudos><span class=secno>12. </span> Tree-Structural
   pseudo-classes</h2>

  <p>Selectors introduces the concept of <dfn
   id=structural-pseudo-classes>structural pseudo-classes</dfn> to permit
   selection based on extra information that lies in the document tree but
   cannot be represented by other simple selectors or combinators.

  <p>Standalone text and other non-element nodes are not counted when
   calculating the position of an element in the list of children of its
   parent. When calculating the position of an element in the list of
   children of its parent, the index numbering starts at 1.

  <h3 id=root-pseudo><span class=secno>12.1. </span> &lsquo;<code
   class=css>:root</code>&rsquo; pseudo-class</h3>

  <p>The <code>:root</code> pseudo-class represents an element that is the
   root of the document. In HTML 4, this is always the <code>HTML</code>
   element.

  <h3 id=nth-child-pseudo><span class=secno>12.2. </span> &lsquo;<code
   class=css>:nth-child()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-child(<var>a</var><code>n</code>+<var>b</var>)</code>
   pseudo-class notation represents an element that has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings <strong>before</strong>
   it in the document tree, for any positive integer or zero value of
   <code>n</code>, and has a parent element. For values of <var>a</var> and
   <var>b</var> greater than zero, this effectively divides the element's
   children into groups of <var>a</var> elements (the last group taking the
   remainder), and selecting the <var>b</var>th element of each group. For
   example, this allows the selectors to address every other row in a table,
   and could be used to alternate the color of paragraph text in a cycle of
   four. The <var>a</var> and <var>b</var> values must be integers (positive,
   negative, or zero). The index of the first child of an element is 1.

  <p>In addition to this, <code>:nth-child()</code> can take &lsquo;<code
   class=css><code>odd</code></code>&rsquo; and &lsquo;<code
   class=css><code>even</code></code>&rsquo; as arguments instead.
   &lsquo;<code class=css><code>odd</code></code>&rsquo; has the same
   signification as <code>2n+1</code>, and &lsquo;<code
   class=css><code>even</code></code>&rsquo; has the same signification as
   <code>2n</code>.

  <p>The argument to <code>:nth-child()</code> must match the grammar below,
   where <code>INTEGER</code> matches the token <code>[0-9]+</code> and the
   rest of the tokenization is given by the <a href="#lex">Lexical
   scanner</a> in section 10.2:

  <pre>nth
    : S* [ ['-'|'+']? INTEGER? {N} [ S* ['-'|'+'] S* INTEGER ]? |
           ['-'|'+']? INTEGER | {O}{D}{D} | {E}{V}{E}{N} ] S*
    ;</pre>

  <div class=example>
   <p>Examples:</p>

   <pre>tr:nth-child(2n+1) /* represents every odd row of an HTML table */
  tr:nth-child(odd)  /* same */
  tr:nth-child(2n+0) /* represents every even row of an HTML table */
  tr:nth-child(even) /* same */

  /* Alternate paragraph colours in CSS */
  p:nth-child(4n+1) { color: navy; }
  p:nth-child(4n+2) { color: green; }
  p:nth-child(4n+3) { color: maroon; }
  p:nth-child(4n+4) { color: purple; }</pre>
  </div>

  <p>When the value <var>b</var> is preceded by a negative sign, the "+"
   character in the expression must be removed (it is effectively replaced by
   the "-" character indicating the negative value of <var>b</var>).

  <div class=example>
   <p>Examples:</p>

   <pre>:nth-child(10n-1)  /* represents the 9th, 19th, 29th, etc, element */
  :nth-child(10n+9)  /* Same */
  :nth-child(10n+-1) /* Syntactically invalid, and would be ignored */</pre>
  </div>

  <p>When <var>a</var>=0, the <var>a</var><code>n</code> part need not be
   included (unless the <var>b</var> part is already omitted). When
   <var>a</var><code>n</code> is not included and <var>b</var> is
   non-negative, the <code>+</code> sign before <var>b</var> (when allowed)
   may also be omitted. In this case the syntax simplifies to
   <code>:nth-child(<var>b</var>)</code>.

  <div class=example>
   <p>Examples:</p>

   <pre>foo:nth-child(0n+5)   /* represents an element foo that is the 5th child
                           of its parent element */
  foo:nth-child(5)      /* same */</pre>
  </div>

  <p>When <var>a</var>=1, or <var>a</var>=-1, the <code>1</code> may be
   omitted from the rule.

  <div class=example>
   <p>Examples:</p>

   <p>The following selectors are therefore equivalent:</p>

   <pre>bar:nth-child(1n+0)   /* represents all bar elements, specificity (0,1,1) */
  bar:nth-child(n+0)    /* same */
  bar:nth-child(n)      /* same */
  bar                   /* same but lower specificity (0,0,1) */</pre>
  </div>

  <p>If <var>b</var>=0, then every <var>a</var>th element is picked. In such
   a case, the +<var>b</var> (or -<var>b</var>) part may be omitted unless
   the <var>a</var> part is already omitted.

  <div class=example>
   <p>Examples:</p>

   <pre>tr:nth-child(2n+0) /* represents every even row of an HTML table */
  tr:nth-child(2n) /* same */</pre>
  </div>

  <p>Whitespace is permitted after the "(", before the ")", and on either
   side of the "+" or "-" that separates the <var>a</var><code>n</code> and
   <var>b</var> parts when both are present.

  <div class=example>
   <p>Valid Examples with white space:</p>

   <pre>
  :nth-child( 3n + 1 )
  :nth-child( +3n - 2 )
  :nth-child( -n+ 6)
  :nth-child( +6 )
  </pre>

   <p>Invalid Examples with white space:</p>

   <pre>
  :nth-child(3 n)
  :nth-child(+ 2n)
  :nth-child(+ 2)
  </pre>
  </div>

  <p>If both <var>a</var> and <var>b</var> are equal to zero, the
   pseudo-class represents no element in the document tree.

  <p>The value <var>a</var> can be negative, but only the positive values of
   <var>a</var><code>n</code>+<var>b</var>, for <code>n</code>&ge;0, may
   represent an element in the document tree.

  <div class=example>
   <p>Example:</p>

   <pre>html|tr:nth-child(-n+6)  /* represents the 6 first rows of XHTML tables */</pre>
  </div>

  <h3 id=nth-last-child-pseudo><span class=secno>12.3. </span> &lsquo;<code
   class=css>:nth-last-child()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-last-child(<var>a</var>n+<var>b</var>)</code>
   pseudo-class notation represents an element that has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings <strong>after</strong>
   it in the document tree, for any positive integer or zero value of
   <code>n</code>, and has a parent element. See <a
   href="#nth-child-pseudo"><code>:nth-child()</code></a> pseudo-class for
   the syntax of its argument. It also accepts the &lsquo;<code
   class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; values as arguments.

  <div class=example>
   <p>Examples:</p>

   <pre>tr:nth-last-child(-n+2)    /* represents the two last rows of an HTML table */

  foo:nth-last-child(odd)    /* represents all odd foo elements in their parent element,
                                counting from the last one */</pre>
  </div>

  <h3 id=nth-of-type-pseudo><span class=secno>12.4. </span> &lsquo;<code
   class=css>:nth-of-type()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-of-type(<var>a</var>n+<var>b</var>)</code> pseudo-class
   notation represents an element that has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings with the same expanded
   element name <strong>before</strong> it in the document tree, for any zero
   or positive integer value of <code>n</code>, and has a parent element. See
   <a href="#nth-child-pseudo"><code>:nth-child()</code></a> pseudo-class for
   the syntax of its argument. It also accepts the &lsquo;<code
   class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; values.

  <div class=example>
   <p>CSS example:</p>

   <p>This allows an author to alternate the position of floated images:</p>

   <pre>img:nth-of-type(2n+1) { float: right; }
  img:nth-of-type(2n) { float: left; }</pre>
  </div>

  <h3 id=nth-last-of-type-pseudo><span class=secno>12.5. </span> &lsquo;<code
   class=css>:nth-last-of-type()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-last-of-type(<var>a</var>n+<var>b</var>)</code>
   pseudo-class notation represents an element that has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings with the same expanded
   element name <strong>after</strong> it in the document tree, for any zero
   or positive integer value of <code>n</code>, and has a parent element. See
   <a href="#nth-child-pseudo"><code>:nth-child()</code></a> pseudo-class for
   the syntax of its argument. It also accepts the &lsquo;<code
   class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; values.

  <div class=example>
   <p>Example:</p>

   <p>To represent all <code>h2</code> children of an XHTML <code>body</code>
    except the first and last, one could use the following selector:</p>

   <pre>body &gt; h2:nth-of-type(n+2):nth-last-of-type(n+2)</pre>

   <p>In this case, one could also use <code>:not()</code>, although the
    selector ends up being just as long:</p>

   <pre>body &gt; h2:not(:first-of-type):not(:last-of-type)</pre>
  </div>

  <h3 id=nth-match><span class=secno>12.6. </span> &lsquo;<code
   class=css>:nth-match()</code>&rsquo; pseudo-class</h3>

  <p><code>:nth-match(<var>a</var>n+<var>b</var> of
   <var>selector-list</var>)</code> pseudo-class notation represents an
   element that has a parent and has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings that match the given
   <var>selector-list</var> <strong>before</strong> it in the document tree,
   for any zero or positive integer value of <code>n</code>.

  <p>See <a href="#nth-child-pseudo"><code>:nth-child()</code></a>
   pseudo-class for the syntax of its <var>a</var>n+<var>b</var> argument,
   which can also be replaced with the &lsquo;<code
   class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; keywords.
   <!-- define <selector>. Split an+b into a similar <notation> -->

  <h3 id=nth-last-match><span class=secno>12.7. </span> &lsquo;<code
   class=css>:nth-last-match()</code>&rsquo; pseudo-class</h3>

  <p><code>:nth-last-match(<var>a</var>n+<var>b</var> of
   <var>selector-list</var>)</code> pseudo-class notation represents an
   element that has a parent and has
   <var>a</var><code>n</code>+<var>b</var>-1 siblings that match the given
   <var>selector-list</var> <strong>after</strong> it in the document tree,
   for any zero or positive integer value of <code>n</code>.

  <p>See <a href="#nth-child-pseudo"><code>:nth-child()</code></a>
   pseudo-class for the syntax of its <var>a</var>n+<var>b</var> argument,
   which can also be replaced with the &lsquo;<code
   class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; keywords.

  <h3 id=first-child-pseudo><span class=secno>12.8. </span> &lsquo;<code
   class=css>:first-child</code>&rsquo; pseudo-class</h3>

  <p>Same as <code>:nth-child(1)</code>. The <code>:first-child</code>
   pseudo-class represents an element that is the first child of some other
   element.

  <div class=example>
   <p>Examples:</p>

   <p>The following selector represents a <code>p</code> element that is the
    first child of a <code>div</code> element:</p>

   <pre>div &gt; p:first-child</pre>

   <p>This selector can represent the <code>p</code> inside the
    <code>div</code> of the following fragment:</p>

   <pre>&lt;p&gt; The last P before the note.&lt;/p&gt;
  &lt;div class="note"&gt;
     &lt;p&gt; The first P inside the note.&lt;/p&gt;
  &lt;/div&gt;</pre>
   but cannot represent the second <code>p</code> in the following fragment:
   <pre>&lt;p&gt; The last P before the note.&lt;/p&gt;
  &lt;div class="note"&gt;
     &lt;h2&gt; Note &lt;/h2&gt;
     &lt;p&gt; The first P inside the note.&lt;/p&gt;
  &lt;/div&gt;</pre>

   <p>The following two selectors are usually equivalent:</p>

   <pre>* &gt; a:first-child /* a is first child of any element */
  a:first-child /* Same (assuming a is not the root element) */</pre>
  </div>

  <h3 id=last-child-pseudo><span class=secno>12.9. </span> &lsquo;<code
   class=css>:last-child</code>&rsquo; pseudo-class</h3>

  <p>Same as <code>:nth-last-child(1)</code>. The <code>:last-child</code>
   pseudo-class represents an element that is the last child of some other
   element.

  <div class=example>
   <p>Example:</p>

   <p>The following selector represents a list item <code>li</code> that is
    the last child of an ordered list <code>ol</code>.

   <pre>ol &gt; li:last-child</pre>
  </div>

  <h3 id=first-of-type-pseudo><span class=secno>12.10. </span> &lsquo;<code
   class=css>:first-of-type</code>&rsquo; pseudo-class</h3>

  <p>Same as <code>:nth-of-type(1)</code>. The <code>:first-of-type</code>
   pseudo-class represents an element that is the first sibling of its type
   in the list of children of its parent element.

  <div class=example>
   <p>Example:</p>

   <p>The following selector represents a definition title <code>dt</code>
    inside a definition list <code>dl</code>, this <code>dt</code> being the
    first of its type in the list of children of its parent element.</p>

   <pre>dl dt:first-of-type</pre>

   <p>It is a valid description for the first two <code>dt</code> elements in
    the following example but not for the third one:</p>

   <pre>&lt;dl&gt;
   &lt;dt&gt;gigogne&lt;/dt&gt;
   &lt;dd&gt;
    &lt;dl&gt;
     &lt;dt&gt;fus&eacute;e&lt;/dt&gt;
     &lt;dd&gt;multistage rocket&lt;/dd&gt;
     &lt;dt&gt;table&lt;/dt&gt;
     &lt;dd&gt;nest of tables&lt;/dd&gt;
    &lt;/dl&gt;
   &lt;/dd&gt;
  &lt;/dl&gt;</pre>
  </div>

  <h3 id=last-of-type-pseudo><span class=secno>12.11. </span> &lsquo;<code
   class=css>:last-of-type</code>&rsquo; pseudo-class</h3>

  <p>Same as <code>:nth-last-of-type(1)</code>. The
   <code>:last-of-type</code> pseudo-class represents an element that is the
   last sibling of its type in the list of children of its parent element.

  <div class=example>
   <p>Example:</p>

   <p>The following selector represents the last data cell <code>td</code> of
    a table row <code>tr</code>.</p>

   <pre>tr &gt; td:last-of-type</pre>
  </div>

  <h3 id=only-child-pseudo><span class=secno>12.12. </span> &lsquo;<code
   class=css>:only-child</code>&rsquo; pseudo-class</h3>

  <p>Represents an element that has a parent element and whose parent element
   has no other element children. Same as
   <code>:first-child:last-child</code> or
   <code>:nth-child(1):nth-last-child(1)</code>, but with a lower
   specificity.

  <h3 id=only-of-type-pseudo><span class=secno>12.13. </span> &lsquo;<code
   class=css>:only-of-type</code>&rsquo; pseudo-class</h3>

  <p>Represents an element that has a parent element and whose parent element
   has no other element children with the same expanded element name. Same as
   <code>:first-of-type:last-of-type</code> or
   <code>:nth-of-type(1):nth-last-of-type(1)</code>, but with a lower
   specificity.

  <h3 id=empty-pseudo><span class=secno>12.14. </span> &lsquo;<code
   class=css>:empty</code>&rsquo; pseudo-class</h3>

  <p>The <code>:empty</code> pseudo-class represents an element that has no
   children at all. In terms of the document tree, only element nodes and
   content nodes (such as DOM <a href="#DOM-LEVEL-3-CORE"
   rel=biblioentry>[DOM-LEVEL-3-CORE]<!--{{DOM-LEVEL-3-CORE}}--></a> text
   nodes, CDATA nodes, and entity references) whose data has a non-zero
   length must be considered as affecting emptiness; comments, processing
   instructions, and other nodes must not affect whether an element is
   considered empty or not.

  <div class=example>
   <p>Examples:</p>

   <p><code>p:empty</code> is a valid representation of the following
    fragment:</p>

   <pre>&lt;p&gt;&lt;/p&gt;</pre>

   <p><code>foo:empty</code> is not a valid representation for the following
    fragments:</p>

   <pre>&lt;foo&gt;bar&lt;/foo&gt;</pre>

   <pre>&lt;foo&gt;&lt;bar&gt;bla&lt;/bar&gt;&lt;/foo&gt;</pre>

   <pre>&lt;foo&gt;this is not &lt;bar&gt;:empty&lt;/bar&gt;&lt;/foo&gt;</pre>
  </div>

  <h2 id=table-pseudos><span class=secno>13. </span> Grid-Structural
   Selectors</h2>

  <p>The double-association of a cell in a 2D grid (to its row and column)
   cannot be represented by parentage in a hierarchical markup language. Only
   one of those associations can be represented hierarchically: the other
   must be explicitly or implicitly defined in the document language
   semantics. In both HTML and DocBook, two of the most common hierarchical
   markup languages, the markup is row-primary (that is, the row associations
   are represented hierarchically); the columns must be implied. Thus the
   <code>:nth-column()</code>, <code>:nth-last-column()</code>, and
   <code>:column()</code> are defined. In a column-primary format, these
   pseudo-classes would match against row associations instead.

  <h3 id=column-pseudo><span class=secno>13.1. </span> &lsquo;<code
   class=css>:column()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:column(<var>selector-list</var>)</code> pseudo-class notation
   represents a cell element belonging to a column that is represented by the
   element selected by its argument. Column membership is determined based on
   the semantics of the document language only: whether and how the elements
   are presented is not considered. If a cell element belongs to more than
   one column, it is represented by a selector indicating any of those
   columns.

  <div class=example>
   <p>The following example makes cells C, E, and G yellow.</p>

   <pre>:column(col.selected) { background: yellow; }</pre>

   <pre>
<!-- -->&lt;table>
<!-- -->  &lt;col span="2">
<!-- -->  &lt;col class="selected">
<!-- -->  &lt;tr>&lt;td>A &lt;td>B &lt;td>C
<!-- -->  &lt;tr>&lt;td span="2">D &lt;td>E
<!-- -->  &lt;tr>&lt;td>F &lt;td span="2">G
<!-- -->&lt;/table></pre>
  </div>

  <h3 id=nth-column-pseudo><span class=secno>13.2. </span> &lsquo;<code
   class=css>:nth-column()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-column(<var>a</var>n+<var>b</var>)</code> pseudo-class
   notation represents a cell element belonging to a column that has
   <var>a</var><code>n</code>+<var>b</var>-1 columns <strong>before</strong>
   it, for any positive integer or zero value of <code>n</code>. Column
   membership is determined based on the semantics of the document language
   only: whether and how the elements are presented is not considered. If a
   cell element belongs to more than one column, it is represented by a
   selector indicating any of those columns.

  <p>See <a href="#nth-child-pseudo"><code>:nth-child()</code></a>
   pseudo-class for the syntax of its argument. It also accepts the
   &lsquo;<code class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; values as arguments.

  <h3 id=nth-last-column-pseudo><span class=secno>13.3. </span> &lsquo;<code
   class=css>:nth-last-column()</code>&rsquo; pseudo-class</h3>

  <p>The <code>:nth-column(<var>a</var>n+<var>b</var>)</code> pseudo-class
   notation represents a cell element belonging to a column that has
   <var>a</var><code>n</code>+<var>b</var>-1 columns <strong>after</strong>
   it, for any positive integer or zero value of <code>n</code>. Column
   membership is determined based on the semantics of the document language
   only: whether and how the elements are presented is not considered. If a
   cell element belongs to more than one column, it is represented by a
   selector indicating any of those columns.

  <p>See <a href="#nth-child-pseudo"><code>:nth-child()</code></a>
   pseudo-class for the syntax of its argument. It also accepts the
   &lsquo;<code class=css><code>even</code></code>&rsquo; and &lsquo;<code
   class=css><code>odd</code></code>&rsquo; values as arguments.

  <h2 id=combinators><span class=secno>14. </span> Combinators</h2>

  <h3 id=descendant-combinators><span class=secno>14.1. </span> Descendant
   combinator</h3>

  <p>At times, authors may want selectors to describe an element that is the
   descendant of another element in the document tree (e.g., "an
   <code>EM</code> element that is contained within an <code>H1</code>
   element"). Descendant combinators express such a relationship. A
   descendant combinator is <a href="#whitespace">whitespace</a> that
   separates two compound selectors. A selector of the form "<code>A
   B</code>" represents an element <code>B</code> that is an arbitrary
   descendant of some ancestor element <code>A</code>.

  <div class=example>
   <p>Examples:</p>

   <p>For example, consider the following selector:</p>

   <pre>h1 em</pre>

   <p>It represents an <code>em</code> element being the descendant of an
    <code>h1</code> element. It is a correct and valid, but partial,
    description of the following fragment:</p>

   <pre>&lt;h1&gt;This &lt;span class="myclass"&gt;headline
  is &lt;em&gt;very&lt;/em&gt; important&lt;/span&gt;&lt;/h1&gt;</pre>

   <p>The following selector:</p>

   <pre>div * p</pre>

   <p>represents a <code>p</code> element that is a grandchild or later
    descendant of a <code>div</code> element. Note the whitespace on either
    side of the "*" is not part of the universal selector; the whitespace is
    a combinator indicating that the <code>div</code> must be the ancestor of
    some element, and that that element must be an ancestor of the
    <code>p</code>.</p>

   <p>The following selector, which combines descendant combinators and <a
    href="#attribute-selectors">attribute selectors</a>, represents an
    element that (1) has the <code>href</code> attribute set and (2) is
    inside a <code>p</code> that is itself inside a <code>div</code>:</p>

   <pre>div p *[href]</pre>
  </div>

  <h3 id=child-combinators><span class=secno>14.2. </span> Child combinators</h3>

  <p>A <dfn id=child-combinator>child combinator</dfn> describes a childhood
   relationship between two elements. A child combinator is made of the
   &quot;greater-than sign&quot; (U+003E, <code>&gt;</code>) character and
   separates two compound selectors.

  <div class=example>
   <p>Examples:</p>

   <p>The following selector represents a <code>p</code> element that is
    child of <code>body</code>:</p>

   <pre>body &gt; p</pre>

   <p>The following example combines descendant combinators and child
    combinators.</p>

   <pre>div ol&gt;li p</pre>
   <!-- LEAVE THOSE SPACES OUT! see below -->
   <p>It represents a <code>p</code> element that is a descendant of an
    <code>li</code> element; the <code>li</code> element must be the child of
    an <code>ol</code> element; the <code>ol</code> element must be a
    descendant of a <code>div</code>. Notice that the optional white space
    around the "&gt;" combinator has been left out.</p>
  </div>

  <p>For information on selecting the first child of an element, please see
   the section on the <code><a
   href="#structural-pseudos">:first-child</a></code> pseudo-class above.

  <h3 id=adjacent-sibling-combinators><span class=secno>14.3. </span>
   Adjacent sibling combinator</h3>

  <p>The adjacent sibling combinator is made of the &quot;plus sign&quot;
   (U+002B, <code>+</code>) character that separates two compound selectors.
   The elements represented by the two compound selectors share the same
   parent in the document tree and the element represented by the first
   compound selector immediately precedes the element represented by the
   second one. Non-element nodes (e.g. text between elements) are ignored
   when considering the adjacency of elements.

  <div class=example>
   <p>Examples:</p>

   <p>The following selector represents a <code>p</code> element immediately
    following a <code>math</code> element:</p>

   <pre>math + p</pre>

   <p>The following selector is conceptually similar to the one in the
    previous example, except that it adds an attribute selector &mdash; it
    adds a constraint to the <code>h1</code> element, that it must have
    <code>class="opener"</code>:</p>

   <pre>h1.opener + h2</pre>
  </div>

  <h3 id=general-sibling-combinators><span class=secno>14.4. </span> General
   sibling combinator</h3>

  <p>The general sibling combinator is made of the &quot;tilde&quot; (U+007E,
   <code>~</code>) character that separates two compound selectors. The
   elements represented by the two compound selectors share the same parent
   in the document tree and the element represented by the first compound
   selector precedes (not necessarily immediately) the element represented by
   the second one.

  <div class=example>
   <p>Example:</p>

   <pre>h1 ~ pre</pre>

   <p>represents a <code>pre</code> element following an <code>h1</code>. It
    is a correct and valid, but partial, description of:</p>

   <pre>&lt;h1&gt;Definition of the function a&lt;/h1&gt;
  &lt;p&gt;Function a(x) has to be applied to all figures in the table.&lt;/p&gt;
  &lt;pre&gt;function a(x) = 12x/13.5&lt;/pre&gt;</pre>
  </div>

  <h3 id=idref-combinators><span class=secno>14.5. </span> Reference
   combinators</h3>

  <p>The IDREF combinator consists of two slashes with an indetervening <a
   href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
   name</a>, and separates two compound selectors, e.g. <code>A /attr/
   B</code>. The elements represented by the two compound seletors are
   related in that an element represented by the first compound selector has
   an ID-reference to the element represented by the second compound
   selector. The ID reference can be given as either an IDREF or a fragment
   URL: the reference is valid as long as the value of the attribute named in
   the combinator consists of either the ID alone or a hash mark (#) followed
   by the ID. Attribute matching for reference combinators follow the same
   rules as for <a
   href="http://www.w3.org/TR/css3-selectors/#attribute-selectors">attribute
   selectors</a>.

  <div class=example>
   <p>The following example highlights an <code>&lt;input&gt;</code> element
    when its <a
    href="http://www.w3.org/TR/html40/interact/forms.html#h-17.9"><code>&lt;label&gt;</code></a>
    is focused or hovered-over:</p>

   <pre>label:matches(:hover, :focus) /for/ input,       /* association by "for" attribute */
<!--  -->label:matches(:hover, :focus):not([for]) input { /* association by containment */
<!--  -->  box-shadow: yellow 0 0 10px; }</pre>
  </div>

  <p class=issue>This could also be implemented as a functional pseudo-class.

  <h2 id=specificity><span class=secno>15. </span> Calculating a selector's
   specificity</h2>

  <p>A selector's specificity is calculated as follows:

  <ul>
   <li>count the number of ID selectors in the selector (= a)

   <li>count the number of class selectors, attributes selectors, and
    pseudo-classes in the selector (= b)

   <li>count the number of type selectors and pseudo-elements in the selector
    (= c)

   <li>ignore the universal selector
  </ul>

  <p>The specificity of a <a href="#negation">negation</a> or <a
   href="#matches">matches</a> pseudo-class is the specificity of its most
   specific argument. The pseudo-class itself does not count as pseudo-class.
   

  <p class=issue>It would probably be better to have match-sensitive
   specificity, if possible. See <a
   href="http://lists.w3.org/Archives/Public/www-style/2010Sep/0534.html">dbaron's
   message</a>.

  <p>Concatenating the three numbers a-b-c (in a number system with a large
   base) gives the specificity.

  <div class=example>
   <p>Examples:</p>

   <pre>*               /* a=0 b=0 c=0 -&gt; specificity =   0 */
  LI              /* a=0 b=0 c=1 -&gt; specificity =   1 */
  UL LI           /* a=0 b=0 c=2 -&gt; specificity =   2 */
  UL OL+LI        /* a=0 b=0 c=3 -&gt; specificity =   3 */
  H1 + *[REL=up]  /* a=0 b=1 c=1 -&gt; specificity =  11 */
  UL OL LI.red    /* a=0 b=1 c=3 -&gt; specificity =  13 */
  LI.red.level    /* a=0 b=2 c=1 -&gt; specificity =  21 */
  #x34y           /* a=1 b=0 c=0 -&gt; specificity = 100 */
  #s12:not(FOO)   /* a=1 b=0 c=1 -&gt; specificity = 101 */
  </pre>
  </div>

  <p class=note><strong>Note:</strong> Repeated occurrances of the same
   simple selector are allowed and do increase specificity.

  <p class=note><strong>Note:</strong> the specificity of the styles
   specified in an HTML <code>style</code> attribute is described in CSS 2.1.
   <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.

  <h2 id=formal-syntax><span class=secno>16. </span> Formal Syntax</h2>

  <p class=issue>This section needs to be updated.

  <h3 id=grammar><span class=secno>16.1. </span> Grammar</h3>

  <p>The grammar below defines the syntax of Selectors. It is globally LL(1)
   and can be locally LL(2) (but note that most UAs should not use it
   directly, since it doesn't express the parsing conventions). The format of
   the productions is optimized for human consumption and some shorthand
   notations beyond Yacc (see <a href="#YACC"
   rel=biblioentry>[YACC]<!--{{!YACC}}--></a>) are used:

  <ul>
   <li><b>*</b>: 0 or more

   <li><b>+</b>: 1 or more

   <li><b>?</b>: 0 or 1

   <li><b>|</b>: separates alternatives

   <li><b>[ ]</b>: grouping
  </ul>

  <p>The productions are:

  <pre>selectors_group
    : selector [ COMMA S* selector ]*
    ;

  selector
    : compound_selector [ combinator simple_selector_sequence ]*
    ;

  combinator
    /* combinators can be surrounded by whitespace */
    : PLUS S* | GREATER S* | TILDE S* | S+
    ;

  simple_selector_sequence
    : [ type_selector | universal ]
      [ HASH | class | attrib | pseudo | negation ]*
    | [ HASH | class | attrib | pseudo | negation ]+
    ;

  type_selector
    : [ namespace_prefix ]? element_name
    ;

  namespace_prefix
    : [ IDENT | '*' ]? '|'
    ;

  element_name
    : IDENT
    ;

  universal
    : [ namespace_prefix ]? '*'
    ;

  class
    : '.' IDENT
    ;

  attrib
    : '[' S* [ namespace_prefix ]? IDENT S*
          [ [ PREFIXMATCH |
              SUFFIXMATCH |
              SUBSTRINGMATCH |
              '=' |
              INCLUDES |
              DASHMATCH ] S* [ IDENT | STRING ] S*
          ]? ']'
    ;

  pseudo
    /* '::' starts a pseudo-element, ':' a pseudo-class */
    /* Exceptions: :first-line, :first-letter, :before and :after. */
    /* Note that pseudo-elements are restricted to one per selector and */
    /* occur only in the last compound_selector. */
    : ':' ':'? [ IDENT | functional_pseudo ]
    ;

  functional_pseudo
    : FUNCTION S* expression ')'
    ;

  expression
    /* In CSS3, the expressions are identifiers, strings, */
    /* or of the form "an+b" */
    : [ [ PLUS | '-' | DIMENSION | NUMBER | STRING | IDENT ] S* ]+
    ;

  negation
    : NOT S* negation_arg S* ')'
    ;

  negation_arg
    : type_selector | universal | HASH | class | attrib | pseudo
    ;</pre>

  <h3 id=lex><span class=secno>16.2. </span> Lexical scanner</h3>

  <p>The following is the tokenizer, written in Flex (see <a href="#FLEX"
   rel=biblioentry>[FLEX]<!--{{!FLEX}}--></a>) notation. The tokenizer is
   case-insensitive.

  <p>The two occurrences of "\377" represent the highest character number
   that current versions of Flex can deal with (decimal 255). They should be
   read as "\4177777" (decimal 1114111), which is the highest possible code
   point in Unicode/ISO-10646. <a href="#UNICODE"
   rel=biblioentry>[UNICODE]<!--{{!UNICODE}}--></a>

  <pre>%option case-insensitive

  ident     [-]?{nmstart}{nmchar}*
  name      {nmchar}+
  nmstart   [_a-z]|{nonascii}|{escape}
  nonascii  [^\0-\177]
  unicode   \\[0-9a-f]{1,6}(\r\n|[ \n\r\t\f])?
  escape    {unicode}|\\[^\n\r\f0-9a-f]
  nmchar    [_a-z0-9-]|{nonascii}|{escape}
  num       [0-9]+|[0-9]*\.[0-9]+
  string    {string1}|{string2}
  string1   \"([^\n\r\f\\"]|\\{nl}|{nonascii}|{escape})*\"
  string2   \'([^\n\r\f\\']|\\{nl}|{nonascii}|{escape})*\'
  invalid   {invalid1}|{invalid2}
  invalid1  \"([^\n\r\f\\"]|\\{nl}|{nonascii}|{escape})*
  invalid2  \'([^\n\r\f\\']|\\{nl}|{nonascii}|{escape})*
  nl        \n|\r\n|\r|\f
  w         [ \t\r\n\f]*

  D         d|\\0{0,4}(44|64)(\r\n|[ \t\r\n\f])?
  E         e|\\0{0,4}(45|65)(\r\n|[ \t\r\n\f])?
  N         n|\\0{0,4}(4e|6e)(\r\n|[ \t\r\n\f])?|\\n
  O         o|\\0{0,4}(4f|6f)(\r\n|[ \t\r\n\f])?|\\o
  T         t|\\0{0,4}(54|74)(\r\n|[ \t\r\n\f])?|\\t
  V         v|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?|\\v

  %%

  [ \t\r\n\f]+     return S;

  "~="             return INCLUDES;
  "|="             return DASHMATCH;
  "^="             return PREFIXMATCH;
  "$="             return SUFFIXMATCH;
  "*="             return SUBSTRINGMATCH;
  {ident}          return IDENT;
  {string}         return STRING;
  {ident}"("       return FUNCTION;
  {num}            return NUMBER;
  "#"{name}        return HASH;
  {w}"+"           return PLUS;
  {w}"&gt;"           return GREATER;
  {w}","           return COMMA;
  {w}"~"           return TILDE;
  ":"{N}{O}{T}"("  return NOT;
  @{ident}         return ATKEYWORD;
  {invalid}        return INVALID;
  {num}%           return PERCENTAGE;
  {num}{ident}     return DIMENSION;
  "&lt;!--"           return CDO;
  "--&gt;"            return CDC;

  \/\*[^*]*\*+([^/*][^*]*\*+)*\/                    /* ignore comments */

  .                return *yytext;</pre>

  <h2 id=profiling><span class=secno>17. </span> Profiles</h2>

  <p>Each specification using Selectors must define the subset of Selectors
   it allows and excludes, and describe the local meaning of all the
   components of that subset.

  <h3 id=css-profiles><span class=secno>17.1. </span> CSS Profiles</h3>

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

  <p>

  <p>In CSS, selectors express pattern matching rules that determine which
   style rules apply to elements in the document tree.

  <p>The following selector (CSS level 2) will <b>match</b> all anchors
   <code>a</code> with attribute <code>name</code> set inside a section 1
   header <code>h1</code>:

  <pre>h1 a[name]</pre>

  <p>All CSS declarations attached to such a selector are applied to elements
   matching it.

  <table class=tprofile>
   <caption>CSS Level 1 Selectors Profile</caption>

   <tbody>
    <tr>
     <th>Specification

     <td><a href="http://www.w3.org/TR/CSS1/">CSS level 1</a>

    <tr>
     <th>Accepts

     <td>type selectors<br>
      class selectors<br>
      ID selectors<br>
      :link, :visited and :active pseudo-classes<br>
      descendant combinator <br>
      ::first-line and ::first-letter pseudo-elements

    <tr>
     <th>Excludes

     <td>namespace prefixes

    <tr>
     <th>Extra constraints

     <td>only one class selector allowed per compound selector,
      pseudo-elements only accept one-colon syntax
  </table>

  <table class=tprofile>
   <caption>CSS Level 2 Selectors Profile</caption>

   <tbody>
    <tr>
     <th>Specification

     <td><a href="http://www.w3.org/TR/CSS2/">CSS level 2</a>

    <tr>
     <th>Accepts

     <td>type selectors<br>
      universal selector<br>
      attribute presence and values selectors<br>
      class selectors<br>
      ID selectors<br>
      :link, :visited, :active, :hover, :focus, :lang() and :first-child
      pseudo-classes <br>
      descendant combinator<br>
      child combinator<br>
      adjacent sibling combinator<br>
      ::first-line and ::first-letter pseudo-elements<br>
      ::before and ::after pseudo-elements

    <tr>
     <th>Excludes

     <td>namespaces, case-insensitive attribute selectors

    <tr>
     <th>Extra constraints

     <td>pseudo-elements only accept one-colon syntax
  </table>

  <h3 id=stts-profile><span class=secno>17.2. </span> STTS Profiles</h3>

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

  <p>Selectors can be used in STTS 3 in two different manners:

  <ol>
   <li>a selection mechanism equivalent to CSS selection mechanism:
    declarations attached to a given selector are applied to elements
    matching that selector,

   <li>fragment descriptions that appear on the right side of declarations.
  </ol>

  <table class=tprofile>
   <caption>STTS3 Selectors Profile</caption>

   <tbody>
    <tr>
     <th>Specification

     <td><a href="http://www.w3.org/TR/NOTE-STTS3">STTS 3</a>

    <tr>
     <th>Accepts

     <td>type selectors<br>
      universal selectors<br>
      attribute selectors<br>
      class selectors<br>
      ID selectors<br>
      level 3 structural pseudo-classes<br>
      all combinators except reference combinator<br>
      namespaces

    <tr>
     <th>Excludes

     <td>namespaces, case-insensitive attribute selectors

    <tr>
     <th>Extra constraints

     <td>some selectors and combinators are not allowed in fragment
      descriptions on the right side of STTS declarations.
  </table>

  <h2 id=conformance><span class=secno>18. </span> Conformance</h2>

  <h3 id=conventions><span class=secno>18.1. </span>Document Conventions</h3>

  <p>Conformance requirements are expressed with a combination of descriptive
   assertions and RFC 2119 terminology. The key words “MUST”, “MUST
   NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”,
   “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the
   normative parts of this document are to be interpreted as described in RFC
   2119. However, for readability, these words do not appear in all uppercase
   letters in this specification.

  <p>All of the text of this specification is normative except sections
   explicitly marked as non-normative, examples, and notes. <a
   href="#RFC2119" rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>

  <p>Examples in this specification are introduced with the words “for
   example” or are set apart from the normative text with
   <code>class="example"</code>, like this:

  <div class=example>
   <p>This is an example of an informative example.</p>
  </div>

  <p>Informative notes begin with the word “Note” and are set apart from
   the normative text with <code>class="note"</code>, like this:

  <p class=note>Note, this is an informative note.

  <h3 id=conformance-classes><span class=secno>18.2. </span> Conformance
   Classes</h3>

  <p>Conformance to Selectors Level 4 is defined for three conformance
   classes:

  <dl>
   <dt><dfn id=selector-instance title="selector instance!!as conformance
    class">selector instance</dfn>

   <dd>A written selector.

   <dt><dfn id=interpreter>interpreter</dfn>

   <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
    that interprets the semantics of a selector.

   <dt><dfn id=authoring-tool>authoring tool</dfn>

   <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
    that writes a style sheet.
  </dl>

  <p>A selector instance is conformant to Selectors Level 4 if it is valid
   according to the selector syntax rules defined in this specification.

  <p>An interpreter is conformant to Selectors Level 4 if it parses
   interprets selectors according to the semantics defined in Selectors Level
   4 (including following the error-handling rules). However, the inability
   of a user agent to implement part of this specification due to the
   limitations of a particular device (e.g., non interactive user agents will
   probably not implement dynamic pseudo-classes because they make no sense
   without interactivity) does not imply non-conformance.

  <p>An authoring tool is conformant to Selectors Level 4 if it writes
   syntactically correct selectors.

  <p>Any specification reusing Selectors must contain a <a
   href="#profiling">Profile</a> listing the subset of Selectors it accepts
   or excludes, and describing any constraints it adds to the current
   specification.

  <p>Specifications reusing Selectors must define how to handle invalid
   selectors. (In the case of CSS, the entire rule in which the selector is
   used is effectively dropped.)

  <h3 id=partial><span class=secno>18.3. </span> Partial Implementations</h3>

  <p>So that authors can exploit the forward-compatible parsing rules to
   trigger fallback behavior, UAs <strong>must</strong> treat as <a
   href="#invalid">invalid</a> any selectors for which they have no usable
   level of support.

  <h3 id=experimental><span class=secno>18.4. </span> Experimental
   Implementations</h3>

  <p>To avoid clashes with future Selectors features, the Selectors
   specification reserves a <a
   href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
   syntax</a> for proprietary extensions to Selectors. The CSS Working Group
   recommends that experimental implementations of features in Selectors
   Working Drafts also use vendor-prefixed pseudo-element or pseudo-class
   names. This avoids any incompatibilities with future changes in the draft.
   Once a specification reaches the Candidate Recommendation stage,
   implementors should implement the non-prefixed syntax for any feature they
   consider to be correctly implemented according to spec.</p>
  <!--
  <h2 id=Tests>Tests</h2>

  <p>This specification has <a
  href="http://www.w3.org/Style/CSS/Test/CSS3/Selectors/current/">a test
  suite</a> allowing user agents to verify their basic conformance to
  the specification. This test suite does not pretend to be exhaustive
  and does not cover all possible combined cases of Selectors.</p>
-->

  <h2 id=acknowledgements><span class=secno>19. </span> Acknowledgements</h2>

  <p>The CSS working group would like to thank everyone who contributed to
   the <a href="http://www.w3.org/TR/css3-selectors">previous Selectors</a>
   specifications over the years, as those specifications formed the basis
   for this one.

  <p>In particular, the working group would like to extend special thanks to
   the following for their specific contributions to Selectors Level 4: L.
   David Baron, Andrew Fedoniouk, Ian Hickson, Grey Hodge, Lachlan Hunt,
   Jason Cranford Teague

  <h2 id=references><span class=secno>20. </span> References</h2>

  <h3 id=normative-references><span class=secno>20.1. </span> 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=CSS21>[CSS21]

   <dd>Bert Bos; et al. <a
    href="http://www.w3.org/TR/2011/REC-CSS2-20110607/"><cite>Cascading Style
    Sheets Level 2 Revision 1 (CSS&#160;2.1) Specification.</cite></a> 7 June
    2011. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2011/REC-CSS2-20110607/">http://www.w3.org/TR/2011/REC-CSS2-20110607/</a>
    </dd>
   <!---->

   <dt id=CSS3NAMESPACE>[CSS3NAMESPACE]

   <dd>Elika J. Etemad; Anne van Kesteren. <a
    href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/"><cite>CSS
    Namespaces Module.</cite></a> 23 May 2008. W3C Candidate Recommendation.
    (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/">http://www.w3.org/TR/2008/CR-css3-namespace-20080523/</a>
    </dd>
   <!---->

   <dt id=FLEX>[FLEX]

   <dd><cite>Flex: The Lexical Scanner Generator.</cite> Version 2.3.7, ISBN
    1882114213</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/PR-css3-selectors-20091215"><cite>Selectors
    Level 3.</cite></a> 15 December 2009. W3C Proposed Recommendation. (Work
    in progress.) URL: <a
    href="http://www.w3.org/TR/2009/PR-css3-selectors-20091215">http://www.w3.org/TR/2009/PR-css3-selectors-20091215</a>
    </dd>
   <!---->

   <dt id=UNICODE>[UNICODE]

   <dd>The Unicode Consortium. <a
    href="http://www.unicode.org/standard/versions/enumeratedversions.html"><cite>The
    Unicode Standard.</cite></a> 2003. Defined by: The Unicode Standard,
    Version 4.0 (Boston, MA, Addison-Wesley, ISBN 0-321-18578-1), as updated
    from time to time by the publication of new versions URL: <a
    href="http://www.unicode.org/standard/versions/enumeratedversions.html">http://www.unicode.org/standard/versions/enumeratedversions.html</a>
    </dd>
   <!---->

   <dt id=YACC>[YACC]

   <dd>S. C. Johnson. <cite>YACC - Yet another compiler compiler.</cite>
    Murray Hill. 1975. Technical Report.</dd>
   <!---->
  </dl>
  <!--end-normative-->

  <h3 id=informative-references><span class=secno>20.2. </span> 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=BCP47>[BCP47]

   <dd>A. Phillips; M. Davis. <a
    href="ftp://ftp.rfc-editor.org/in-notes/bcp/bcp47.txt"><cite>Tags for
    Identifying Languages.</cite></a> September 2009. BCP 47. Internet Best
    Current Practice. Currently represented by RFC 5646. URL: <a
    href="ftp://ftp.rfc-editor.org/in-notes/bcp/bcp47.txt">ftp://ftp.rfc-editor.org/in-notes/bcp/bcp47.txt</a>
    </dd>
   <!---->

   <dt id=CSS3UI>[CSS3UI]

   <dd>Tantek &#199;elik. <a
    href="http://www.w3.org/TR/2004/CR-css3-ui-20040511"><cite>CSS3 Basic
    User Interface Module.</cite></a> 11 May 2004. W3C Candidate
    Recommendation. (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2004/CR-css3-ui-20040511">http://www.w3.org/TR/2004/CR-css3-ui-20040511</a>
    </dd>
   <!---->

   <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=HTML401>[HTML401]

   <dd>Dave Raggett; Arnaud Le Hors; Ian Jacobs. <a
    href="http://www.w3.org/TR/1999/REC-html401-19991224"><cite>HTML 4.01
    Specification.</cite></a> 24 December 1999. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/1999/REC-html401-19991224">http://www.w3.org/TR/1999/REC-html401-19991224</a>
    </dd>
   <!---->

   <dt id=HTML5>[HTML5]

   <dd>Ian Hickson. <a
    href="http://www.w3.org/TR/2011/WD-html5-20110525/"><cite>HTML5.</cite></a>
    25 May 2011. W3C Working Draft. (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2011/WD-html5-20110525/">http://www.w3.org/TR/2011/WD-html5-20110525/</a>
    </dd>
   <!---->

   <dt id=MATHML>[MATHML]

   <dd>Patrick Ion; Robert Miner. <a
    href="http://www.w3.org/1999/07/REC-MathML-19990707"><cite>Mathematical
    Markup Language (MathML) 1.01 Specification.</cite></a> 7 July 1999. W3C
    Recommendation. URL: <a
    href="http://www.w3.org/1999/07/REC-MathML-19990707">http://www.w3.org/1999/07/REC-MathML-19990707</a>
    </dd>
   <!---->

   <dt id=SELECTORS-API2>[SELECTORS-API2]

   <dd>Lachlan Hunt. <a
    href="http://www.w3.org/TR/2010/WD-selectors-api2-20100119/"><cite>Selectors
    API Level 2.</cite></a> 19 January 2010. W3C Working Draft. (Work in
    progress.) URL: <a
    href="http://www.w3.org/TR/2010/WD-selectors-api2-20100119/">http://www.w3.org/TR/2010/WD-selectors-api2-20100119/</a>
    </dd>
   <!---->

   <dt id=STTS3>[STTS3]

   <dd>Daniel Glazman. <a href="http://www.w3.org/TR/NOTE-STTS3"><cite>Simple
    Tree Transformation Sheets 3.</cite></a> Electricit&#233; de France. 11
    November 1998. Submission to the W3C. URL: <a
    href="http://www.w3.org/TR/NOTE-STTS3">http://www.w3.org/TR/NOTE-STTS3</a>
    </dd>
   <!---->

   <dt id=SVG11>[SVG11]

   <dd>Erik Dahlstr&#246;m; et al. <a
    href="http://www.w3.org/TR/2011/PR-SVG11-20110609/"><cite>Scalable Vector
    Graphics (SVG) 1.1 (Second Edition).</cite></a> 9 June 2011. W3C Proposed
    Recommendation. (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2011/PR-SVG11-20110609/">http://www.w3.org/TR/2011/PR-SVG11-20110609/</a>
    </dd>
   <!---->

   <dt id=XFORMS10>[XFORMS10]

   <dd>John M. Boyer. <a
    href="http://www.w3.org/TR/2009/REC-xforms-20091020/"><cite>XForms
    1.1.</cite></a> 20 October 2009. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2009/REC-xforms-20091020/">http://www.w3.org/TR/2009/REC-xforms-20091020/</a>
    </dd>
   <!---->

   <dt id=XML-NAMES>[XML-NAMES]

   <dd>Tim Bray; et al. <a
    href="http://www.w3.org/TR/2009/REC-xml-names-20091208/"><cite>Namespaces
    in XML 1.0 (Third Edition).</cite></a> 8 December 2009. W3C
    Recommendation. URL: <a
    href="http://www.w3.org/TR/2009/REC-xml-names-20091208/">http://www.w3.org/TR/2009/REC-xml-names-20091208/</a>
    </dd>
   <!---->

   <dt id=XML10>[XML10]

   <dd>C. M. Sperberg-McQueen; et al. <a
    href="http://www.w3.org/TR/2008/REC-xml-20081126/"><cite>Extensible
    Markup Language (XML) 1.0 (Fifth Edition).</cite></a> 26 November 2008.
    W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2008/REC-xml-20081126/">http://www.w3.org/TR/2008/REC-xml-20081126/</a>
    </dd>
   <!---->
  </dl>
  <!--end-informative-->