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<div class="head"><p><a href="http://www.w3.org/"><img height="48" alt="W3C" src="http://www.w3.org/Icons/w3c_home" width="72"></a>
</p><h1><span class="modulename">Selectors</span></h1>
  <h2>W3C Candidate Recommendation 13 November 2001</h2>
  <dl>
    <dt>This version:
    </dt><dd><a href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113">
                 http://www.w3.org/TR/2001/CR-css3-selectors-20011113</a>
    </dd><dt>Latest version:
    </dt><dd><a href="http://www.w3.org/TR/css3-selectors">
                 http://www.w3.org/TR/css3-selectors</a>
    </dd><dt>Previous version:
    </dt><dd><a href="http://www.w3.org/TR/2001/WD-css3-selectors-20010126">
                 http://www.w3.org/TR/2001/WD-css3-selectors-20010126</a>
    </dd><dt><a name="editors-list"></a>Editors:
    </dt><dd><a href="mailto:glazman@netscape.com">Daniel Glazman</a> (<span class="company"><a href="http://www.netscape.com/">Netscape/AOL</a></span>)
    </dd><dd><a href="mailto:tantekc@microsoft.com">Tantek Çelik</a> (<span class="company"><a href="http://www.microsoft.com/">Microsoft Corporation</a></span>)
    </dd><dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>
    </dd><dd>Peter Linss (former editor, formerly of&nbsp;<span class="company"><a href="http://www.netscape.com/">Netscape/AOL</a></span>)
    </dd><dd>John Williams (former editor, <span class="company"><a href="http://www.quark.com/">Quark, Inc.</a></span>) 
  </dd></dl>
<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#Copyright">Copyright</a>
©2001 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.lcs.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.inria.fr/"><abbr lang="fr" title="Institut National de Recherche en Informatique et Automatique">INRIA</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#Legal_Disclaimer">liability</a>,
<a href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#W3C_Trademarks">trademark</a>,
<a href="http://www.w3.org/Consortium/Legal/copyright-documents-19990405">document
use</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-software-19980720">software
licensing</a> rules apply.
</p><hr title="Separator for header">
</div>

<h2><a name="abstract"></a>Abstract</h2>
<p><acronym title="Cascading Style Sheets">CSS</acronym> (Cascading Style Sheets) is a language for describing the rendering of
  <acronym title="Hypertext Markup Language">HTML</acronym> and <acronym title="Extensible Markup Language">XML</acronym>
  documents on screen, on paper, in speech, etc. To bind style properties
  to elements in the document, CSS uses <em>selectors,</em> which are patterns
  that match one or more elements. This document describes the selectors that are proposed
  for CSS level 3. It includes and extends the selectors of CSS level 2. 
</p><h2><a name="status"></a>Status of this document</h2>
<p>This document is one of the "modules" of the upcoming CSS3 specification. It
  not only describes the selectors that already exist in <a href="#CSS1"><abbr title="CSS level 1">CSS1</abbr></a> and <a href="#CSS2"><abbr title="CSS level 2">CSS2</abbr></a>,
  but also proposes new selectors for <abbr title="CSS level 3">CSS3</abbr> as well as for
  other languages that may need them. The CSS Working Group doesn't expect that all
  implementations of CSS3 will have to implement all selectors. Instead,
  there will probably be a small number of variants of CSS3, so-called "profiles".
  For example, it may be that only a profile for non-interactive user agents
  will include all of the proposed selectors. 
</p><p>This specification is being put forth as a <a href="http://www.w3.org/TR/#About">Candidate
  Recommendation</a> by the <a href="http://www.w3.org/Style/Group">CSS Working
  Group</a>. This document is a revision of the <a href="http://www.w3.org/TR/2001/WD-css3-selectors-20010126">Working
  Draft dated 2001 January 26</a>, and has incorporated suggestions received
  during last call review, comments, and further deliberations of the W3C CSS
  Working Group.
</p><p>The duration of Candidate Recommendation is expected to last approximately
  six months (ending <strong>May, 2002</strong>). All persons are encouraged
  to review and implement this specification and return comments to the (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public mailing
  list <a href="http://www.w3.org/Mail/Lists.html#www-style">www-style</a> (see <a href="http://www.w3.org/Mail/Request">instructions</a>).
  W3C Members can also send comments directly to the CSS Working Group. 
</p><p>Should this specification prove impossible to implement, the Working Group
  will return the document to Working Draft status and make necessary changes.
  Otherwise, the Working Group anticipates asking the W3C Director to advance
  this document to Proposed Recommendation.
</p><p>This is still a draft document and may be updated, replaced, or obsoleted by
  other documents at any time. It is inappropriate to cite a W3C Candidate Recommendation
  as other than "work in progress." A list of current W3C working drafts
  can be found at <a href="http://www.w3.org/TR">http://www.w3.org/TR</a>.<br>
  <br>
  This document may be available in <a href="http://www.w3.org/Style/css3-selectors-updates/translations">translation</a>.
  The English version of this specification is the only normative version.
</p><h2><a name="dependencies"></a>Dependencies with other CSS3 Modules</h2>
<ul>
  <li>General Syntax
  </li><li>Value Assignment, Cascade and Inheritance
  </li><li>Generated Content / Markers
  </li><li>User Interface
</li></ul>
<div class="subtoc">
<h2><a name="contents">Table of contents</a></h2>
<ul class="toc">
  <li class="tocline2"><a href="#context">1.
  Context</a>
  <ul>
    <li><a href="#changesFromCSS2">1.1
    Changes from CSS2</a> </li></ul>
  </li><li class="tocline2"><a href="#selectors">2.
  Selectors</a>
  </li><li class="tocline2"><a href="#casesens">3.
  Case sensitivity</a>
  </li><li class="tocline2"><a href="#selector-syntax">4. Selector
  syntax</a>
  </li><li class="tocline2"><a href="#grouping">5.
  Groups of selectors</a>
  </li><li class="tocline2"><a href="#simple-selectors">6. Simple
  selectors</a>
  <ul class="toc">
    <li class="tocline3"><a href="#type-selectors">6.1 Type
    selectors</a>
    <ul class="toc">
      <li class="tocline4"><a href="#typenmsp">6.1.1 Type selectors
      and Namespaces</a> </li></ul>
    </li><li class="tocline3"><a href="#universal-selector">6.2 Universal
    selector</a>
    <ul>
      <li><a href="#univnmsp">6.2.1
      Universal selector and Namespaces</a> </li></ul>
    </li><li class="tocline3"><a href="#attribute-selectors">6.3
    Attribute selectors</a>
    <ul class="toc">
      <li class="tocline4"><a href="#attribute-representation">6.3.1
      Representation of attributes and attributes values</a>
      </li><li><a href="#attribute-substrings">6.3.2
      Substring matching attribute selectors</a>
      </li><li class="tocline4"><a href="#attrnmsp">6.3.3 Attribute
      selectors and Namespaces</a>
      </li><li class="tocline4"><a href="#def-values">6.3.4 Default
      attribute values in DTDs</a> </li></ul>
    </li><li class="tocline3"><a href="#class-html">6.4 Class
    selectors</a>
    </li><li class="tocline3"><a href="#id-selectors">6.5 ID
    selectors</a>
    </li><li class="tocline3"><a href="#pseudo-classes">6.6
    Pseudo-classes</a>
    <ul class="toc">
      <li class="tocline4"><a href="#dynamic-pseudos">6.6.1 Dynamic
      pseudo-classes</a>
      </li><li class="tocline4"><a href="#target-pseudo">6.6.2 The
      :target pseudo-class</a>
      </li><li class="tocline4"><a href="#lang-pseudo">6.6.3 The :lang()
      pseudo-class</a>
      </li><li class="tocline4"><a href="#UIstates">6.6.4 UI element
      states pseudo-classes</a>
      </li><li class="tocline4"><a href="#structural-pseudos">6.6.5
      Structural pseudo-classes</a>
      <ul>
        <li><a href="#root-pseudo">:root
        pseudo-class</a>
        </li><li><a href="#nth-child-pseudo">:nth-child()
        pseudo-class</a>
        </li><li><a href="#nth-last-child-pseudo">:nth-last-child()</a>

        </li><li><a href="#nth-of-type-pseudo">:nth-of-type()
        pseudo-class</a>
        </li><li><a href="#nth-last-of-type-pseudo">:nth-last-of-type()</a>

        </li><li><a href="#first-child-pseudo">:first-child
        pseudo-class</a>
        </li><li><a href="#last-child-pseudo">:last-child
        pseudo-class</a>
        </li><li><a href="#first-of-type-pseudo">:first-of-type
        pseudo-class</a>
        </li><li><a href="#last-of-type-pseudo">:last-of-type
        pseudo-class</a>
        </li><li><a href="#only-child-pseudo">:only-child
        pseudo-class</a>
        </li><li><a href="#only-of-type-pseudo">:only-of-type
        pseudo-class</a>
        </li><li><a href="#empty-pseudo">:empty
        pseudo-class</a> </li></ul>
      </li><li class="tocline4"><a href="#content-selectors">6.6.6
      Content pseudo-class</a>
      </li><li><a href="#negation">6.6.7 The
      negation pseudo-class</a> </li></ul></li></ul>
  </li><li><a href="#pseudo-elements">7.
  Pseudo-elements</a>
  <ul>
    <li><a href="#first-line">7.1 The
    :first-line pseudo-element</a>
    </li><li><a href="#first-letter">7.2 The
    :first-letter pseudo-element</a>
    </li><li><a href="#UIfragments">7.3 UI
    element fragments pseudo-elements</a>
    </li><li><a href="#gen-content">7.4 The
    :before and :after pseudo-elements</a> </li></ul>
  </li><li class="tocline2"><a href="#combinators">8. Combinators</a>
  <ul class="toc">
    <li class="tocline3"><a href="#descendant-combinators">8.1
    Descendant combinators</a>
    </li><li class="tocline3"><a href="#child-combinators">8.2 Child
    combinators</a>
    </li><li class="tocline3"><a href="#adjacent-combinators">8.3
    Adjacent sibling combinators</a>
    <ul class="toc">
      <li class="tocline4"><a href="#adjacent-d-combinators">8.3.1
      Adjacent direct combinators</a>
      </li><li class="tocline4"><a href="#adjacent-i-combinators">8.3.2
      Adjacent indirect combinators</a> </li></ul></li></ul>
  </li><li class="tocline2"><a href="#specificity">9. Calculating a
  selector's specificity</a>
  </li><li class="tocline2"><a href="#w3cselgrammar">10. The grammar of
  <span class="modulename">Selectors</span></a>
  <ul class="toc">
    <li class="tocline3"><a href="#grammar">10.1 Grammar</a>
    </li><li class="tocline3"><a href="#lex">10.2
    Lexical scanner</a> </li></ul>
  </li><li class="tocline2"><a href="#downlevel">11. Namespaces and
  Down-Level clients</a>
  </li><li class="tocline2"><a href="#profiling">12. Profiles</a>
  </li><li><a href="#Conformance">13. Conformance
  and Requirements</a>
  </li><li><a href="#Tests">14. Tests</a>
  </li><li><a href="#ACKS">15.
  Acknowledgements</a>
  </li><li class="tocline2"><a href="#references">16. References</a> <!--<li class="tocline2"><a href="#changes">Changes from previous version</a>--></li></ul></div>
<h2><a name="context">1. Context</a></h2>
<p>Members of the CSS+FP Working Group proposed during the Clamart meeting to
modularize the CSS specification. 
</p><p>This modularization, and the externalization of the general syntax of CSS
will reduce the size of the specification and allow new specifications
to use selectors and/or CSS general syntax. For instance, behaviors or tree
transformations. 
</p><p>This specification contains its own <a href="#Tests">test cases</a>, one test per concept introduced in this document.
  These tests are not full conformance tests but are intended to provide users
  with a way to check if a part of this specification is implemented <i>ad minima</i>
  or is not implemented at all.
</p><h3><a name="changesFromCSS2"></a>1.1 Changes from CSS2</h3>
<p>The main differences between the selectors in CSS2 and those in
 <span class="modulename">Selectors</span> are:
</p><ul>
  <li>the list of basic definitions (selector, group of selectors, simple
  selector, etc.) has been clarified
  </li><li>an optional namespace component is now allowed in type element selectors,
  the universal selector and attribute selectors
  </li><li>a new combinator
  </li><li>new simple selectors including substring matching attribute selectors, and new
  pseudo-classes
  </li><li>new pseudo-elements, and introduction of the "::" convention for pseudo-elements
  </li><li>a rewriting of the selectors grammar
  </li><li>profiles to be added to specifications integrating <span class="modulename">Selectors</span> and
  defining the set of selectors which is actually supported by each
  specification
  </li><li><span class="modulename">Selectors</span> are now a CSS3 Module and an independent specification.
  Other  specifications can now refer to this document independently of CSS
  </li><li>the specification now contains its own test suite. </li>
</ul>
<h2><a name="selectors"></a>2. Selectors</h2>
<p>A <span class="propernoun">Selector</span> 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><p><span class="propernoun">Selectors</span> may range from simple element names to rich contextual
representations. 
</p><p>The following table summarizes <span class="propernoun">Selector</span> syntax: 
</p><table class="selectorsreview" width="100%" border="1">
  <tbody>
  <tr>
    <th class="pattern">Pattern</th>
    <th class="meaning">Meaning</th>
    <th class="described">Described in section</th>
    <th class="origin">First defined in CSS level</th></tr>
  <tr>
    <td class="pattern">*</td>
    <td class="meaning">any element</td>
    <td class="described"><a href="#universal-selector">Universal
      selector</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E</td>
    <td class="meaning">an element of type E</td>
    <td class="described"><a href="#type-selectors">Type selector</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E[foo]</td>
    <td class="meaning">an E element with a "foo" attribute</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E[foo="bar"]</td>
    <td class="meaning">an E element whose "foo" attribute value is exactly
      equal to "bar"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E[foo~="bar"]</td>
    <td class="meaning">an E element whose "foo" attribute value is a list of
      space-separated values, one of which is exactly equal to "bar"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E[foo^="bar"]</td>
    <td class="meaning">an E element whose "foo" attribute value begins exactly
      with the string "bar"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E[foo$="bar"]</td>
    <td class="meaning">an E element whose "foo" attribute value ends exactly
      with the string "bar"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E[foo*="bar"]</td>
    <td class="meaning">an E element whose "foo" attribute value contains the
      substring "bar"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E[hreflang|="en"]</td>
    <td class="meaning">an E element whose "hreflang" attribute has a hyphen-separated
      list of values beginning (from the left) with "en"</td>
    <td class="described"><a href="#attribute-selectors">Attribute
      selectors</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E:root</td>
    <td class="meaning">an E element, root of the document</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:nth-child(n)</td>
    <td class="meaning">an E element, the n-th child of its parent</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:nth-last-child(n)</td>
    <td class="meaning">an E element, the n-th child of its parent, counting
      from the last one</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:nth-of-type(n)</td>
    <td class="meaning">an E element, the n-th sibling of its type</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:nth-last-of-type(n)</td>
    <td class="meaning">an E element, the n-th sibling of its type, counting
      from the last one</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:first-child</td>
    <td class="meaning">an E element, first child of its parent</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E:last-child</td>
    <td class="meaning">an E element, last child of its parent</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:first-of-type</td>
    <td class="meaning">an E element, first sibling of its type</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:last-of-type</td>
    <td class="meaning">an E element, last sibling of its type</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:only-child</td>
    <td class="meaning">an E element, only child of its parent</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:only-of-type</td>
    <td class="meaning">an E element, only sibling of its type</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:empty</td>
    <td class="meaning">an E element that has no children (including text
    nodes)</td>
    <td class="described"><a href="#structural-pseudos">Structural
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:link <br>E:visited</td>
    <td class="meaning">an E element being the source anchor of a hyperlink of
      which the target is not yet visited (:link) or already visited
    (:visited)</td>
    <td class="described"><a href="#link">The link
      pseudo-classes</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E:active <br>E:hover <br>E:focus</td>
    <td class="meaning">an E element during certain user actions</td>
    <td class="described"><a href="#useraction-pseudos">The user
      action pseudo-classes</a></td>
    <td class="origin">1 and 2</td></tr>
  <tr>
    <td class="pattern">E:target</td>
    <td class="meaning">an E element being the target of the referring URI</td>
    <td class="described"><a href="#target-pseudo">The target
      pseudo-class</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:lang(fr)</td>
    <td class="meaning">an element of type E in language "fr" (the document
      language specifies how language is determined)</td>
    <td class="described"><a href="#lang-pseudo">The :lang()
      pseudo-class&nbsp;</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E:enabled<br>E:disabled&nbsp;</td>
    <td class="meaning">a user interface element E which is enabled or
    disabled</td>
    <td class="described"><a href="#UIstates">The UI element states
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:checked<br>E:indeterminate&nbsp;</td>
    <td class="meaning">a user interface element E which is checked or in an
      indeterminate state (for instance a radio-button or checkbox)</td>
    <td class="described"><a href="#UIstates">The UI element states
      pseudo-classes</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E:contains("foo")</td>
    <td class="meaning">an E element containing the substring "foo" in its textual
      contents</td>
    <td class="described"><a href="#content-selectors">Content
      pseudo-class</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E::first-line</td>
    <td class="meaning">the first formatted line of an E element</td>
    <td class="described"><a href="#first-line">The :first-line
      pseudo-element</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E::first-letter</td>
    <td class="meaning">the first formatted letter of an E element</td>
    <td class="described"><a href="#first-letter">The :first-letter
      pseudo-element</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E::selection</td>
    <td class="meaning">the portion of an E element that is currently
      selected/highlighted by the user</td>
    <td class="described"><a href="#UIfragments">The UI element
      fragments pseudo-elements</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E::before</td>
    <td class="meaning">generated content before an E element</td>
    <td class="described"><a href="#gen-content">The :before
      pseudo-element</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E::after</td>
    <td class="meaning">generated content after an E element</td>
    <td class="described"><a href="#gen-content">The :after
      pseudo-element</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E.warning</td>
    <td class="meaning">an E element whose class is
"warning" (the document language specifies how class is determined).</td>
    <td class="described"><a href="#class-html">Class
    selectors</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E#myid</td>
    <td class="meaning">an E element with ID equal to "myid".</td>
    <td class="described"><a href="#id-selectors">ID
    selectors</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E:not(s)</td>
    <td class="meaning">an E element that does not match simple selector s</td>
    <td class="described"><a href="#negation">Negation
      pseudo-class</a></td>
    <td class="origin">3</td></tr>
  <tr>
    <td class="pattern">E F</td>
    <td class="meaning">an F element descendant of an E element</td>
    <td class="described"><a href="#descendant-combinators">Descendant
      combinator</a></td>
    <td class="origin">1</td></tr>
  <tr>
    <td class="pattern">E &gt; F</td>
    <td class="meaning">an F element child of an E element</td>
    <td class="described"><a href="#child-combinators">Child
      combinator</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E + F</td>
    <td class="meaning">an F element immediately preceded by an E element</td>
    <td class="described"><a href="#adjacent-d-combinators">Direct
      adjacent combinator</a></td>
    <td class="origin">2</td></tr>
  <tr>
    <td class="pattern">E ~ F</td>
    <td class="meaning">an F element preceded by an E element</td>
    <td class="described"><a href="#adjacent-i-combinators">Indirect
      adjacent combinator</a></td>
    <td class="origin">3</td></tr></tbody></table>
<p>The meaning of each selector is derived from the table above by
 prepending "matches" to the contents of each cell of the "Meaning" column.
</p><h2><a name="casesens">3. Case sensitivity</a></h2>
<p>The case-sensitivity of document language element names in selectors depends
on the document language. For example, in HTML, element names are
case-insensitive, but in XML they are case-sensitive. 
</p><p>The case-sensitivity of attribute names and attribute values in attribute
selectors also depends on the document language.
</p><h2><a name="selector-syntax">4. Selector syntax</a></h2>
<p>A&nbsp;<dfn><a name="selector">selector</a></dfn> is a chain of one or more <a href="#sequence">sequences of simple
selectors</a> separated by <a href="#combinators">combinators</a>. 
</p><p>A&nbsp;<dfn><a name="sequence">sequence of simple selectors</a></dfn> is a chain
  of <a href="#simple-selectors-dfn">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 <a href="#universal-selector">universal
  selector</a>. No other type selector or universal selector is allowed in the
  sequence. 
</p><p>A&nbsp;<dfn><a name="simple-selectors-dfn"></a><a href="#simple-selectors">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="#id-selectors">ID
  selector</a>, <a href="#content-selectors">content selector</a>, or <a href="#pseudo-classes">pseudo-class</a>. One <a href="#pseudo-elements">pseudo-element</a> may be appended to the last sequence
  of simple selectors.
</p><p><dfn>Combinators</dfn> are: white space, "greater-than sign" (<code>&gt;</code>),
  "plus sign" (<code>+</code>) and "tilde" (<code>~</code>).
  White space may appear between a combinator and the simple selectors around
  it. <a name="whitespace"></a>Only the characters "space" (Unicode code 32), "tab"
  (9), "line feed" (10), "carriage return" (13), and "form feed" (12) can occur
  in white space. Other space-like characters, such as "em-space" (8195) and "ideographic
  space" (12288), are never part of white space.
</p><p>The elements of the document tree represented by a selector are called <dfn><a name="subject"></a>subjects
  of the selector</dfn>. A selector consisting of a single sequence of simple
  selectors represents any element satisfying its requirements. Prepending another
  sequence of simple selectors and a combinator to a sequence imposes additional
  matching constraints, so the subjects of a selector are always a subset of the
  elements represented by the rightmost sequence of simple selectors.
</p><p><strong><em>Note</em></strong><em>: an empty selector, containing no sequence
  of simple selectors and no combinator, is an <a href="#Conformance">invalid
  selector</a>.</em>
</p><h2><a name="grouping">5. Groups of selectors</a></h2>
<p>When several selectors share the same declarations, they may be grouped into
a comma-separated list. 
</p><div class="example">CSS example(s):
<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>is equivalent to: <pre>h1, h2, h3 { font-family: sans-serif }</pre></div>
<p><b>Warning</b>: the equivalence is true in this example because all selectors
  are valid selectors. If just one of these selectors is invalid, the entire group
  of selectors is invalid thus invalidating the rule for all three heading elements,
  whereas only one of the three individual heading rules would be invalid.
  
</p><h2><a name="simple-selectors">6. Simple selectors</a></h2>
<h3><a name="type-selectors">6.1 Type selector</a></h3>
<p>A&nbsp;<dfn>type selector</dfn> is the name of a document language element
type. A type selector represents an instance of the element type in the document
tree. 
</p><div class="example">Example:
  <p>The following selector represents an <code>h1</code> element in the document
tree: </p><pre>h1</pre></div>
<h4><a name="typenmsp">6.1.1 Type selectors and Namespaces</a></h4>
<p>Type selectors allow an optional namespace (<a href="#XMLNAMES">[XML-NAMES]</a>) component.
  A namespace prefix that has been previously declared
  may be prepended to the element name separated by the namespace separator
  "vertical bar" (<code>|</code>). The namespace component may be left
  empty to indicate that the selector is only to represent elements with no declared
  namespace. Furthermore, an asterisk may be used for the namespace prefix, indicating
  that the selector represents elements in any namespace (including elements
  with no namespace). 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 declared. In that case, the selector will represent only
  elements in the default namespace.
</p><p>Note : a type selector containing a namespace prefix that has not been previously
 declared is an <a href="#Conformance">invalid</a> selector.
 The mechanism for declaring a namespace prefix is left up to the language
 implementing <span class="modulename">Selectors</span>.
 In CSS, such a mechanism is defined in the General Syntax module.

<!--<p>An alternative approach would be to define element type selectors that have
  no namespace component to match only elements that have no namespace (unless
  a default namespace has been declared in the CSS). This would make the selector
  "<code>h1</code>" equivalent to the selector "<code>|h1</code>" as opposed to
  "<code>*|h1</code>". The downside to this approach is that legacy style sheets
  (those written without any namespace constructs) will fail to match in all XML
  documents where namespaces are used throughout, e.g. all XHTML documents. -->
</p><p>It should be noted that if a namespace prefix used in a selector has not been
  previously declared, then the selector must be considered invalid and the entire
  style rule will be ignored in accordance with the <a href="#Conformance">standard
  error handling rules</a>. 
</p><p>It should further be noted that in a namespace aware client, element type
selectors 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>. See <a href="#downlevel">below</a>
for notes about matching behaviors in down-level clients. 
</p><p>In summary:
</p><dl>
  <dt><code>ns|E</code>
  </dt><dd>elements with name E in namespace ns
  </dd><dt><code>*|E</code>
  </dt><dd>elements with name E in any namespace, including those without any
  declared namespace
  </dd><dt><code>|E</code>
  </dt><dd>elements with name E without any declared namespace
  </dd><dt><code>E</code>
  </dt><dd>if no default namespace has been specified, this is equivalent to *|E.
  Otherwise it is equivalent to ns|E where ns is the default namespace. </dd></dl>
<div class="example">
<p>CSS examples: 
  </p><pre>@namespace foo url(http://www.example.com);

foo|h1 { color: blue }

foo|* { color: yellow }

|h1 { color: red }

*|h1 { color: green }

h1 { color: green }</pre>
  <p>The first 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 without any declared
namespace. 
</p><p>The fourth rule will match <code>h1</code> elements in any namespace (including
those without any declared namespace).
</p><p>The last rule is equivalent to the fourth rule because no default namespace
has been defined.</p></div>
<h3><a name="universal-selector">6.2 Universal selector</a> </h3>
<p>The&nbsp;<dfn>universal selector</dfn>, written "asterisk" (<code>*</code>),
  represents the qualified name of any element type. It represents then any single
  element in the document tree in any namespace (including those without any declared
  namespace) if no default namespace has been specified. If a default namespace
  has been specified, see <a href="#univnmsp">Universal selector and Namespaces</a> below.
</p><p>If the universal selector is not the only component of a sequence of simple
selectors, the <code>*</code> may be omitted. For example: 
</p><div class="example">
<ul>
  <li><code>*[hreflang|=en]</code> and <code>[hreflang|=en]</code> are equivalent,
  </li><li><code>*.warning</code> and <code>.warning</code> are equivalent,
  </li><li><code>*#myid</code> and <code>#myid</code> are equivalent. </li></ul></div>
<p><b>Note</b>: it is recommended that the <code>*</code>, representing the
universal selector, not be omitted.
</p><h4><a name="univnmsp">6.2.1 Universal selector and Namespaces</a></h4>
<p>The universal selector allows an optional namespace component.
</p><dl>
  <dt><code>ns|*</code>
  </dt><dd>all elements in namespace ns
  </dd><dt><code>*|*</code>
  </dt><dd>all elements
  </dd><dt><code>|*</code>
  </dt><dd>all elements without any declared namespace
  </dd><dt><code>*</code>
  </dt><dd>if no default namespace has been specified, this is equivalent to *|*.
  Otherwise it is equivalent to ns|* where ns is the default namespace. </dd></dl>
<p>Note: a universal selector containing a namespace prefix that has not been
 previously declared is an <a href="#Conformance">invalid</a> selector.
 The mechanism for declaring a namespace prefix is left up to the language
 implementing <span class="modulename">Selectors</span>.
 In CSS, such a mechanism is defined in the General Syntax module.

</p><h3><a name="attribute-selectors">6.3 Attribute selectors</a></h3>
<p><span class="propernoun">Selectors</span> allow the representation of an element's attributes.

</p><h4><a name="attribute-representation">6.3.1 Attribute presence and values
selectors</a></h4>
<p>CSS2 introduced four attribute selectors:
</p><dl>
  <dt><code>[att]</code>
  </dt><dd>Represents the <code>att</code> attribute, whatever the value of the
  attribute.
  </dd><dt><code>[att=val]</code>
  </dt><dd>Represents the <code>att</code> attribute with value exactly "val".
  </dd><dt><code>[att~=val]</code>
  </dt><dd>Represents the <code>att</code> attribute whose value is a space-separated list of words,
  one of which is exactly "val". If this selector is used, the
  words in the value must not contain spaces (since they are separated by
  spaces).
  </dd><dt><code>[att|=val]</code>
  </dt><dd>Represents the <code>att</code> attribute, its value either being exactly "val" or
  beginning with "val" immediately followed by "-".
  This is primarily intended to allow language subcode matches
  (e.g., the <code>hreflang</code> attribute on the <code>link</code> element in HTML)
  as described in RFC 3066 (<a class="noxref" href="#rfc3066" rel="biblioentry">[RFC3066]</a>).
   Note: 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>.
  
</dd></dl>
<p>Attribute values must be identifiers or strings. The case-sensitivity of
attribute names and values in selectors depends on the document language. 
</p><div class="example">Examples:
  <p>For example, 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>
  Multiple attribute selectors can be used to represent several attributes of
  an element, or several conditions on the same attribute.
  <p>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 selectors illustrate the differences between "=" and "~=".
    The first selector will represent, for example, the value "copyright copyleft
    copyeditor" on a <code>rel</code> attribute. The second selector will only
    represent 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 a <code>link</code> element whose
  <code>hreflang</code> attribute is exactly "fr".
  </p><pre>link[hreflang=fr]</pre>
  <p>The following selector represents a <code>link</code> element for which the
    values of the <code>hreflang</code> attribute begins with "en", including
    "en", "en-US", and "en-cockney":
  </p><pre>link[hreflang|="en"]</pre>
  <p>Similarly, the following selectors represents a <code>DIALOGUE</code> element
whenever it has one of two different values for an attribute <code>character</code>:
</p><pre>DIALOGUE[character=romeo]&nbsp;

DIALOGUE[character=juliet]</pre></div>
<h4><a name="attribute-substrings"></a>6.3.2 Substring matching attribute
selectors</h4>
<p>Three additional attribute selectors are provided
 for matching substrings in the value of an attribute:
</p><dl>
  <dt><code>[att^=val]</code>
  </dt><dd>Represents the <code>att</code> attribute whose value begins with
  the prefix "val"
  </dd><dt><code>[att$=val]</code>
  </dt><dd>Represents the <code>att</code> attribute whose value ends with the
  suffix "val"
  </dd><dt><code>[att*=val]</code>
  </dt><dd>Represents the <code>att</code> attribute whose value contains at least
  one instance of the substring "val" </dd></dl>
<p>Attribute values must be identifiers or strings. The case-sensitivity of
attribute names in selectors depends on the document language. 
</p><p>Example:
</p><p>The following selector represents an HTML <code>object</code>, referencing an
image:</p><pre>object[type^="image/"]
</pre>
<p>The following selector represents an HTML anchor <code>a</code> with an
  <code>href</code> attribute whose value ends with ".html".
</p><pre>a[href$=".html"]</pre>
<p>The following selector represents a HTML paragraph with a <code>title</code>
attribute whose value contains the substring "hello"</p><pre>p[title*="hello"] </pre>
<h4><a name="attrnmsp">6.3.3 Attribute selectors and Namespaces</a></h4>
<p>Attribute selectors allow an optional namespace component to the attribute
  name. A namespace prefix that has been previously declared may be prepended
  to the attribute name separated by the namespace separator
  "vertical bar" (<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 declared 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><p>Note : an attribute
 selector with an attribute name containing a namespace prefix that has
 not been previously declared is an <a href="#Conformance">invalid</a> selector.
 The mechanism for declaring a namespace prefix is left up to the language
 implementing <span class="modulename">Selectors</span>.
 In CSS, such a mechanism is defined in the General Syntax module.

</p><p>CSS examples: 
</p><div class="example">
  <pre>@namespace foo "http://www.example.com";

[foo|att=val] { color: blue }

[*|att] { color: yellow }

[|att] { color: green }

[att] { color: green }</pre>
  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>The second rule will match only elements with the attribute <code>att</code>
regardless of the namespace of the attribute (including no declared 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 declared to be in a
namespace.</p></div>
<h4><a name="def-values">6.3.4 Default attribute values in DTDs</a></h4>
<p>Attribute selectors represent explicitly set attribute values in the document
  tree. Default attribute values may be defined in a DTD or elsewhere.
  <span class="propernoun">Selectors</span> should be designed so that they work
  even if the default values are not included in the document tree.
</p><div class="example">Examples:
  <p>For example, consider an element <code>EXAMPLE</code> with an attribute
<code>notation</code> that has a default value of "decimal". The DTD fragment
might be </p><pre>&lt;!ATTLIST EXAMPLE notation (decimal,octal) "decimal"&gt;</pre>
  If the selectors represent an <code>EXAMPLE</code> element when the value of
  the attribute is explicitly set:
  <pre>EXAMPLE[notation=decimal]
EXAMPLE[notation=octal]</pre>
  then to represent only the case where this attribute is set by default, and
  not explicitly, the following selector might be used:
  <pre>EXAMPLE:not([notation])</pre>
</div>
<h3><a name="class-html">6.4 Class selectors</a></h3>
<p>Working with HTML, authors may use the period (<code>.</code>) notation as
  an alternative to the <code>~=</code> notation when representing the <code>class</code>
  attribute. Thus, for HTML, <code>div.value</code> and <code>div[class~=value]</code>
  have the same meaning. The attribute value must immediately follow the "period"
  (<code>.</code>). Note: UAs may apply selectors using the period (.) notation
  in XML documents if the UA has namespace specific knowledge that allows it to
  determine which attribute is the "class" attribute for the respective
  namespace. One such example of namespace specific knowledge is the prose in
  the specification for a particular namespace (e.g. SVG 1.0 [<a href="#SVG">SVG</a>]
  describes the <a href="http://www.w3.org/TR/2001/PR-SVG-20010719/styling.html#ClassAttribute">SVG
  "class" attribute</a> and how a UA should interpret it, and similarly
  MathML 1.01 [<a href="#MATH">MATH</a>] describes the <a href="http://www.w3.org/1999/07/REC-MathML-19990707/chapter2.html#sec2.3.4">MathML
  "class" attribute</a>.)
</p><p>
</p><div class="example">Examples:
  <p>For example, we can represent an arbitrary element with
<code>class~="pastoral"</code> as follows: </p><pre>*.pastoral</pre>or just <pre>.pastoral</pre>
  The following selector represents an <code>h1</code> element with <code>class~="pastoral"</code>:
  <pre>h1.pastoral</pre>
  <p>For example, the following selector represents a <code>p</code> element whose
<code>class</code> attribute has been assigned a list of space-separated values that
includes "pastoral" and "marine": </p><pre>p.pastoral.marine</pre>
<p>It is fully identical to:</p><pre>p.marine.pastoral</pre>
  <p>This selector represents for example a <code>p</code> with <code>class="pastoral
    blue aqua marine"</code> or <code>class="marine blue pastoral aqua" </code>but
    not <code>class="pastoral blue"</code>.
</p></div>
<h3><a name="id-selectors">6.5 ID selectors</a></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 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><p>An ID typed attribute of a document language allows authors to assign an identifier
  to one element instance in the document tree. W3C ID selectors represent an
  element instance based on its identifier. An ID selector contains a "number
  sign" (#) immediately followed by the ID value. 
</p><div class="example">Examples:
  <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>
  The following selector represents any element whose ID typed attribute has the
  value "z98y".
  <pre>*#z98y</pre></div>
<div class="note"><i><b>Note.</b> In XML 1.0 <a class="noxref" href="http://www.w3.org/TR/REC-CSS2/refs.html#ref-XML10" rel="biblioentry">[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 designer 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>.
  Elements in XML 1.0 documents without a DTD do not have IDs at all.</i></div>
<h3><a name="pseudo-classes">6.6 Pseudo-classes</a></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><p>A pseudo-class always contains a "colon" (<code>:</code>) followed
  by the name of the pseudo-class and optionally by a value between parentheses.

</p><p>Pseudo-classes are allowed in all sequences of simple selectors contained in
  a selector. Pseudo-classes are allowed anywhere in sequences of simple selectors,
  after the leading type selector or universal selector (possibly omitted). Pseudo-class
  names are case-insensitive. Some pseudo-classes are mutually exclusive, while
  others can be applied simultaneously to the same element. Pseudo-classes may
  be dynamic, in the sense that an element may acquire or lose a pseudo-class
  while a user interacts with the document.
</p><h4><a name="dynamic-pseudos">6.6.1 Dynamic pseudo-classes</a></h4>
<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><p>Dynamic pseudo-classes do not appear in the document source or document tree.

</p><h5>The&nbsp;<a name="link">link pseudo-classes: :link and :visited</a></h5>
<p>User agents commonly display unvisited links differently from previously
visited ones. <span class="modulename">Selectors</span> provides the pseudo-classes <code>:link</code> and
<code>:visited</code> to distinguish them: 
</p><ul>
  <li>The <code>:link</code> pseudo-class applies for links that have not yet been
  visited.
  </li><li>The <code>:visited</code> pseudo-class applies once the link has been visited
  by the user. </li></ul>
<div class="note"><i><b>Note.</b> After some amount of time, user agents may
choose to return a visited link to the (unvisited) ':link' state.</i></div>
<p>The two states are mutually exclusive. 
</p><div class="example">Example:
  <p>The following selector represents links carrying class <code>external</code> and
already visited: </p><pre>a.external:visited</pre></div>
<h5>The&nbsp;<a name="useraction-pseudos">user action pseudo-classes :hover,
:active, and :focus</a></h5>
<p>Interactive user agents sometimes change the rendering in response to user
actions. <span class="modulename">Selectors</span> provides three pseudo-classes for the selection of an
element the user is acting on. 
</p><ul>
  <li>The <code>:hover</code> pseudo-class applies while the user designates an
  element (with some pointing device), but does not 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
  supporting <a href="http://www.w3.org/TR/REC-CSS2/media.html#interactive-media-group">interactive
  media</a> do not have to support this pseudo-class. Some conforming user
  agents supporting <a href="http://www.w3.org/TR/REC-CSS2/media.html#interactive-media-group">interactive
  media</a> may not be able to support this pseudo-class (e.g., a pen device).
  </li><li>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.
  </li><li>The <code>:focus</code> pseudo-class applies while an element has the focus
  (accepts keyboard or mouse events, or other forms of input). </li></ul>
<p>There may be document language or implementation specific limits on which elements can become
<code>:active</code> or acquire <code>:focus</code>. 
<!--
<p>Only elements whose 'user-input' property (see <a
href="#UI-WD">[UI]</a>) has the value of
"enabled" can become <code>:active</code> or acquire <code>:focus</code>. -->
</p><p>These pseudo-classes are not mutually exclusive. An element may match several
of them at the same time. 
</p><div class="example">Examples:
  <pre>a:link&nbsp;&nbsp;&nbsp; /* unvisited links */
a:visited /* visited links&nbsp;&nbsp; */
a:hover&nbsp;&nbsp; /* user hovers&nbsp;&nbsp;&nbsp;&nbsp; */
a:active&nbsp; /* active links&nbsp;&nbsp;&nbsp; */</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 pseudo-class
    :focus and in pseudo-class :hover. 
</p></div>
<div class="note"><i><b>Note.</b> An element can be both ':visited' and ':active'
(or ':link' and ':active').</i></div>
<h4><a name="target-pseudo">6.6.2 The target pseudo-class :target</a></h4>
<p>Some URIs refer to a location within a resource. This kind of URI ends with
  a "number sign" (<code>#</code>) followed by an anchor identifier
  (called the fragment identifier). 
</p><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 section_2 in a HTML document: 
</p><pre>http://example.com/html/top.html#section_2</pre>
<p>A target element can be represented by the <code>:target</code> pseudo-class:

</p><pre>p.note:target</pre>
<p>represents a <code>p</code> of class note that is the target element of the
  referring URI. 
</p><div class="example">CSS example of use of the <code>:target</code> pseudo-class: <pre>*:target { color : red }

*:target::before { content : url(target.png) }</pre></div>
<h4><a name="lang-pseudo">6.6.3 The language pseudo-class :lang</a></h4>
<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="#html40" rel="biblioentry">[HTML4.01]</a>, the language is determined by a combination of
  the <code>lang</code> attribute, the <code>meta</code> element, and possibly
  by information from 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><p>The pseudo-class <code>:lang(C)</code> represents an element that is in language
  C. Here C is a language code as specified in HTML 4.01 <a href="#html40" rel="biblioentry">[HTML4.01]</a> and RFC 3066 <a href="#rfc3066" rel="biblioentry">[RFC3066]</a>.
</p><div class="example">Examples:
  <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>
<h4><a name="UIstates">6.6.4 The UI element states pseudo-classes</a></h4>
<h5><a name="enableddisabled">The :enabled and :disabled pseudo-classes</a></h5>
<p>The purpose of the <code>:enabled</code> pseudo-class is to allow authors to
  customize the look of user interface elements which are enabled - which the
  user can select/activate in some fashion (e.g. clicking on a button with a mouse).
  There is a need for such a pseudo-class because there is no way to programmatically
  specify the default appearance of say, an enabled <code>input</code> element
  without also specifying what it would look like when it was disabled. 
</p><p>Similar to <code>:enabled</code>, <code>:disabled</code> allows the author to specify
precisely how a disabled or inactive user interface element should look. 
</p><p>It should be noted that most elements will be neither enabled nor disabled.
An element is enabled if the user can either activate it or transfer the focus
to it. An element is disabled if it could be enabled, but the user cannot
presently activate it or transfer focus to it. 
</p><h5><a name="checked">The :checked pseudo-class</a></h5>
<p><!--The <code>:checked</code> pseudo-class only applies to elements which are
'user-input: enabled' or 'user-input : disabled' (see [UI] for the 'user-input'
property). -->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. The <code>:checked</code>
pseudo-class initially applies to such elements that have the HTML4
<code>selected</code> attribute 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. While the
<code>:checked</code> pseudo-class is dynamic in nature, and is altered by user
action, since it can also be based on the presence of the semantic HTML4
<code>selected</code> attribute, it applies to all media. 
</p><h5><a name="indeterminate">The :indeterminate pseudo-class</a></h5>
<p><!--The <code>:indeterminate</code> pseudo-class only applies to elements which are
'user-input: enabled' or 'user-input: disabled' (see <a
href="#UI-WD">[UI]</a> for the 'user-input'
property). -->Radio and checkbox elements can be toggled by the user, but are
sometimes in an indeterminate state, neither checked nor unchecked. This can be
due to an element attribute, or DOM manipulation. The <code>:indeterminate</code>
pseudo-class applies to such elements. While the <code>:indeterminate</code>
pseudo-class is dynamic in nature, and is altered by user action, since it can
also be based on the presence of an element attribute, it applies to all media.

</p><p>Components of a radio-group initialized with no pre-selected choice are an
example of :indeterminate state.
</p><h4><a name="structural-pseudos">6.6.5 Structural pseudo-classes</a></h4>
<p><span class="modulename">Selectors</span> introduces the concept of&nbsp;<dfn>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><p>Note that standalone PCDATA 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. 
</p><h5><a name="root-pseudo">:root pseudo-class</a></h5>
<p>The <code>:root</code> pseudo-class represents an element that is the root
  of the document. In HTML 4, this is the <code>HTML</code> element. In XML, it
  is whatever is appropriate for the DTD or schema and namespace for that XML
  document. 
</p><h5><a name="nth-child-pseudo">:nth-child() pseudo-class</a></h5>
<p>The <code>:nth-child(an+b)</code> pseudo-class notation represents an element
  that has an+b-1 siblings <strong>before</strong> it in the document tree, for
  a given positive integer or zero value of n. In other words, this matches the
  bth child of an element after all the children have been split into groups of
  a elements each. For example, this allows the selectors to address every other
  row in a table, and could be used, for example, to alternate the color of paragraph
  text in a cycle of four. The a and b values must be zero, negative integers
  or positive integers. The index of the first child of an element is 1.
</p><p>In addition to this, <code>:nth-child()</code> can take 'odd' and 'even' for
argument. 'odd' has the same signification as 2n+1, and 'even' has the same
signification as 2n. 
</p><div class="example">Examples:
<pre>tr:nth-child(2n+1) /* represents every odd row of a HTML table */
tr:nth-child(odd)  /* same */
tr:nth-child(2n)   /* represents every even row of a 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 a=0, no repeating is used, so for example <code>:nth-child(0n+5)</code>
matches only the fifth child. When a=0, the a part need not be included, so the
syntax simplifies to <code>:nth-child(b)</code> and the last example simplifies
to <code>:nth-child(5)</code>.
</p><div class="example">
<pre>foo:nth-child(0n+1)   /* represents an element foo, first child of its parent element */
foo:nth-child(1)      /* same */</pre>
</div>
<p>When a=1, the number may be omitted from the rule,
so the following examples are equivalent: 
</p><div class="example">
<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 b=0, then every a-th element is picked:
</p><div class="example">
<pre>tr:nth-child(2n) /* represents every even row of a HTML table */</pre>
</div>
<p>If both a and b are equal to zero, the pseudo-class represents no element in
the document tree.
</p><p>The value a can be negative, but only the positive values of an+b, for n&gt;=
  0, may represent an element in the document tree, of course:
</p><div class="example">
<pre>html|tr:nth-child(-n+6)  /* represents the 6 first rows of XHTML tables */</pre>
</div>
<h5><a name="nth-last-child-pseudo">:nth-last-child() pseudo-class</a></h5>
<p>The <code>:nth-last-child(an+b)</code> pseudo-class notation represents an
element that has an+b-1 siblings <strong>after</strong> it in the document tree,
for a given positive integer or zero value of n. See <code>:nth-child()</code>
pseudo-class for the syntax of its argument. It also accepts the 'even' and
'odd' values for argument.
</p><div class="example">Examples: <pre>tr:nth-last-child(-n+2)    /* represents the two last rows of a HTML table */

foo:nth-last-child(odd)    /* represents all odd foo elements in their parent element,
                              counting from the last one */</pre></div>
<h5><a name="nth-of-type-pseudo">:nth-of-type() pseudo-class</a></h5>
<p>The <code>:nth-of-type(an+b)</code> pseudo-class notation represents an element
that has an+b-1 siblings with the same element name <strong>before</strong> it
in the document tree, for a given zero or positive integer value of n. In other
words, this matches the bth child of that type after all the children of that
type have been split into groups of a elements each. See
<code>:nth-child()</code> pseudo-class for the syntax of its argument. It also
accepts the 'even' and 'odd' values for argument.
</p><div class="example">For example, this allows in CSS to alternate the position of
floated images: <pre>img:nth-of-type(2n+1) { float: right; }
img:nth-of-type(2n) { float: left; }
</pre></div>
<h5><a name="nth-last-of-type-pseudo">:nth-last-of-type() pseudo-class</a></h5>
<p>The <code>:nth-last-of-type(an+b)</code> pseudo-class notation represents an
element that has an+b-1 siblings with the same element name
<strong>after</strong> it in the document tree, for a given zero or positive
integer value of n. See <code>:nth-child()</code> pseudo-class for the syntax of
its argument. It also accepts the 'even' and 'odd' values for argument. 
</p><div class="example">For example, to represent all <code>h2</code> children of a
XHTML <code>body</code> except the first and last, one would use the following
selector: <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>
<h5><a name="first-child-pseudo">:first-child pseudo-class</a></h5>
<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.
</p><div class="example">Examples:
  <p>In the following example, the 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>This selector can represent the <code>p</code>
inside the <code>div</code> of the following fragment: <pre>&lt;p&gt; The last P before the note.&lt;/p&gt;
&lt;div class="note"&gt;
&nbsp;&nbsp; &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;
&nbsp;&nbsp; &lt;h2&gt;Note&lt;/h2&gt;
&nbsp;&nbsp; &lt;p&gt; The first P inside the note.&lt;/p&gt;
&lt;/div&gt;</pre>The following two selectors are equivalent: <pre>* &gt; a:first-child&nbsp;&nbsp; /* a is first child of any element */
a:first-child&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* Same */</pre></div>
<h5><a name="last-child-pseudo">:last-child pseudo-class</a></h5>
<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. 
</p><p>The following selector represents a list item <code>li</code> that is the last
child of an ordered list <code>ol</code>. 
</p><div class="example">Example:
<pre>ol &gt; li:last-child</pre></div>
<h5><a name="first-of-type-pseudo">:first-of-type pseudo-class</a></h5>
<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. 
</p><div class="example">Example:
<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>It is a valid description for the first two
<code>dt</code> in the following example but not for the third one: <pre>&lt;dl&gt;&lt;dt&gt;gigogne&lt;/dt&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;dd&gt;&lt;dl&gt;&lt;dt&gt;fus&amp;eacute;e&lt;/dt&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;dd&gt;multistage rocket&lt;/dd&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;dt&gt;table&lt;/dt&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;dd&gt;nest of tables&lt;/dd&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/dl&gt;&lt;/dd&gt;
&lt;/dl&gt;</pre></div>
<h5><a name="last-of-type-pseudo">:last-of-type pseudo-class</a></h5>
<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. 
</p><div class="example">Example:
<p>The following selector represents the last data cell <code>td</code> of a table
row. </p><pre>tr &gt; td:last-of-type</pre></div>
<h5><a name="only-child-pseudo">:only-child pseudo-class</a></h5>
<p>Represents an element that has no siblings. Same as
<code>:first-child:last-child</code> or
<code>:nth-child(1):nth-last-child(1)</code>, but with a lower specificity.
</p><h5><a name="only-of-type-pseudo">:only-of-type pseudo-class</a></h5>
<p>Represents an element that has no siblings with the same 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.

</p><h5><a name="empty-pseudo"></a>:empty pseudo-class</h5>
<p>The <code>:empty</code> pseudo-class represents an element that has no children
  at all, including possibly empty text nodes, from a DOM point of view.
</p><div class="example">Examples:
<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>
<h4><a name="content-selectors">6.6.6 Content pseudo-class</a></h4>
<p>The <code>:contains("foo")</code> pseudo-class notation represents an element
whose textual contents contain the given substring. The argument of this
pseudo-class can be a string (surrounded by double quotes) or a keyword.
</p><p>Usage of the content pseudo-class is restricted to static media types (see
  <a href="#CSS2">[CSS2]</a>).
</p><p>The textual contents of a given element is determined by the concatenation of
all PCDATA contained in the element and sub-elements. 
</p><div class="example">Example: <pre>p:contains("Markup")</pre>is a correct and valid, but partial, description
of: <pre>&lt;p&gt;&lt;strong&gt;H&lt;/strong&gt;yper&lt;strong&gt;t&lt;/strong&gt;ext
&nbsp;&nbsp; &lt;strong&gt;M&lt;/strong&gt;&lt;em&gt;arkup&lt;/em&gt;
&nbsp;&nbsp; &lt;strong&gt;L&lt;/strong&gt;anguage&lt;/p&gt;</pre></div>
<p>Special characters can be inserted in the argument of a content pseudo-class
  using the escape mechanism for Unicode characters and carriage returns.
</p><p><strong>Warning</strong>: the selector <code>ul:contains("chief")</code>
  will match the list <code>&lt;ul&gt;&lt;li&gt;... the greek letter chi&lt;/li&gt;&lt;li&gt;effective&lt;/li&gt;&lt;/ul&gt;</code>
</p><div><i><b>Note</b>: <code>:contains()</code> is a pseudo-class, not a pseudo-element.
  The following CSS rule applied to the HTML fragment above will not add a red
  background only to the word "Markup" but will add such a background to the whole
  paragraph.</i></div>
<pre>P:contains("Markup") { background-color : red }</pre>
<h4><a name="negation"></a>6.6.7 The negation pseudo-class</h4>
<p>The negation pseudo-class is a functional notation taking a <a href="#simple-selectors-dfn">simple selector</a>
(excluding the negation pseudo-class itself and pseudo-elements) as an argument. It
represents an element that is not represented by the argument.
</p><div class="example">
  <p>Examples:
</p><p>The following CSS selector matches all <code>button</code> elements in a 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 group of selectors represents all elements but HTML links.</p><pre>html|*:not(:link):not(:visited)
</pre></div>
<p><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.
</p><h3><a name="pseudo-elements">7. Pseudo-elements</a></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 designers to refer to this otherwise inaccessible
information. Pseudo-elements may also provide designers 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). 
</p><p>A pseudo-element is made of two colons (<code>::</code>) followed by the name of
the pseudo-element.
</p><p><strong>Note</strong>: this <code>::</code> notation is introduced by the current
  document in order to establish a discrimination between pseudo-classes and pseudo-elements.
  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. This compatibility is not allowed for the new pseudo-elements introduced
  in CSS level 3.
</p><p>Pseudo-elements may only appear once in the sequence of simple selectors that
represents the <a href="#subject">subjects</a> of the
selector. 
</p><h4><a name="first-line">7.1 The ::first-line pseudo-element</a></h4>
<p>The <code>::first-line</code> pseudo-element describes the first formatted line
of an element.
</p><p>For instance in CSS:</p><pre class="example">p::first-line { text-transform: uppercase }
</pre>
<p>The above rule means "change the letters of the first line of every paragraph
to uppercase". However, the selector <code>p::first-line</code> does not match
any real HTML element. It does match a pseudo-element that conforming user
agents will insert at the beginning of every paragraph.
</p><p>Note that the length of the first line depends on a number of factors,
including the width of the page, the font size, etc. Thus, an ordinary HTML
paragraph such as:</p><pre class="html-example">&lt;p&gt;This is a somewhat long HTML
paragraph that will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/p&gt;
</pre>
<p>the lines of which happen to be rendered as follows if the style rule above applies:
</p><pre class="html-example">THIS IS A SOMEWHAT LONG HTML PARAGRAPH THAT
will be broken into several lines. The first
line will be identified by a fictional tag
sequence. The other lines will be treated as
ordinary lines in the paragraph.
</pre>
<p>might be "rewritten" by user agents to include the <em>fictional tag sequence</em>
for <code>::first-line</code>. This fictional tag sequence helps to show how properties
are inherited.
</p><pre>&lt;p&gt;<b>&lt;p::first-line&gt;</b> This is a somewhat long HTML
paragraph that<b>&lt;/p::first-line&gt;</b> will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/p&gt;
</pre>
<p>If a pseudo-element breaks up a real element, the desired effect can be
described by closing and then re-opening the fictional tag sequence.
Thus, if we mark up the previous paragraph with a <code>span</code> element:</p><pre>&lt;p&gt;<b>&lt;span class="test"&gt;</b> This is a somewhat<b>&lt;/span&gt;</b> long HTML
paragraph that will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/p&gt;
</pre>
<p>the user agent could generate the appropriate start and end tags for the fictional tag sequence for <code>::first-line</code>.

</p><pre>&lt;p&gt;<b>&lt;span class="test"&gt;</b>&lt;p::first-line&gt; This is a
somewhat&lt;/p::first-line&gt;<b>&lt;/span&gt;</b>&lt;p::first-line&gt;
long HTML paragraph that&lt;/p::first-line&gt; will be broken into
several lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.&lt;/p&gt;
</pre>
<p>The <code>::first-line</code> pseudo-element can only be attached to a
block-level element.
</p><p>The <code>::first-line</code> pseudo-element is similar to an inline-level
element, but with certain restrictions, depending on usage. Only the following
properties apply to a <code>::first-line</code> pseudo-element: font properties,
color properties, background properties, <span class="propinst-word-spacing">'word-spacing',</span> <span class="propinst-letter-spacing">'letter-spacing',</span> <span class="propinst-text-decoration">'text-decoration',</span> <span class="propinst-vertical-align">'vertical-align',</span> <span class="propinst-text-transform">'text-transform',</span> <span class="propinst-line-height">'line-height',</span> <span class="propinst-text-shadow">'text-shadow'</span>, and <span class="propinst-clear">'clear'.</span>
</p><h4><a name="first-letter">7.2 The ::first-letter pseudo-element</a></h4>
<p>The <code>::first-letter</code> pseudo-element describes the first formatted
  letter of an element.
</p><p>The <code>::first-letter</code> pseudo-element can be attached to all elements.

</p><p>The <code>::first-letter</code> pseudo-element may be used for "initial caps" and
"drop caps", which are common typographical effects. This type of initial letter
is similar to an inline-level element if its CSS 'float' property is 'none', but
with certain restrictions, depending on usage. Otherwise it is similar to a
floated element.
</p><p>These are the CSS properties that apply to <code>::first-letter</code>
pseudo-elements: font properties, color properties, background properties,
'text-decoration', 'vertical-align' (only if 'float' is 'none'),
'text-transform', 'line-height', margin properties, padding properties, border
properties, 'float', 'text-shadow', and 'clear'.
</p><div class="html-example">
<p>
</p><p>The following CSS2 will make a drop cap initial letter span two lines:
  </p><pre>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"&gt;
&lt;HTML&gt;
 &lt;HEAD&gt;
  &lt;TITLE&gt;Drop cap initial letter&lt;/TITLE&gt;
  &lt;STYLE type="text/css"&gt;
   P               { font-size: 12pt; line-height: 12pt }
   P::first-letter { font-size: 200%; font-style: italic;
                     font-weight: bold; float: left }
   SPAN            { text-transform: uppercase }
  &lt;/STYLE&gt;
 &lt;/HEAD&gt;
 &lt;BODY&gt;
  &lt;P&gt;&lt;SPAN&gt;The first&lt;/SPAN&gt; few words of an article
    in The Economist.&lt;/P&gt;
 &lt;/BODY&gt;
&lt;/HTML&gt;
</pre>
<p>This example might be formatted as follows:
</p><div class="figure">
<p><img height="54" alt="Image illustrating the combined effect of the :first-letter and :first-line pseudo-elements" src="first-letter.gif" width="105"> </p></div>
<p>The fictional tag sequence is:</p><pre>&lt;P&gt;
&lt;SPAN&gt;
&lt;P::first-letter&gt;
T
&lt;/P::first-letter&gt;he first
&lt;/SPAN&gt;
few words of an article in the Economist.
&lt;/P&gt;
</pre>
<p>Note that the <code>::first-letter</code> pseudo-element tags abut the content
(e.g., the initial character). When both the <code>::first-line</code> and the
<code>::first-letter</code> pseudo-elements are used, the <code>::first-letter</code>
fictional tag sequence is inserted inside the <code>::first-line</code>
fictional tag sequence.</p></div>
<p>In order to achieve traditional drop caps formatting, user agents may
approximate font sizes, for example to align baselines. Also, the glyph outline
may be taken into account when formatting.
</p><p>Punctuation (i.e, characters defined in Unicode <a class="noxref" href="#UNICODE" rel="biblioentry"><span class="normref">[UNICODE]</span></a> in the "open" (Ps), "close" (Pe), and "other"
(Po) punctuation classes), that precedes the first letter should be included, as
in:
</p><div class="figure">
<p><img height="72" alt="Quotes that precede the
first letter should be included." src="first-letter2.gif" width="114"></p></div>
<p>The <code>::first-letter</code> pseudo-element matches parts of elements
only.
</p><p>Some languages may have specific rules about how to treat certain letter combinations.
  In Dutch, for example, if the letter combination "ij" appears at the beginning
  of a word, both letters should be considered within the <code>::first-letter</code>
  pseudo-element. The <code>::first-letter</code> pseudo-element should select
  select from beginning of element up to the first non-opening-punctuation character
  cluster.
</p><p>
</p><div class="example">
<p><a name="overlapping-example">The following example</a> illustrates how
overlapping pseudo-elements may interact. The first letter of each
<code>P</code> element will be green with a font size of '24pt'. The rest of the
first formatted line will be 'blue' while the rest of the paragraph will be
'red'.</p><pre>P { color: red; font-size: 12pt }
P::first-letter { color: green; font-size: 200% }
P::first-line { color: blue }

&lt;P&gt;Some text that ends up on two lines&lt;/P&gt;
</pre>
<p>Assuming that a line break will occur before the word "ends", the fictional
tag sequence for this fragment might be:</p><pre>&lt;P&gt;
&lt;P::first-line&gt;
&lt;P::first-letter&gt;
S
&lt;/P::first-letter&gt;ome text that
&lt;/P::first-line&gt;
ends up on two lines
&lt;/P&gt;
</pre>
<p>Note that the<code>::first-letter</code> element is inside the
<code>::first-line</code> element. Properties set on <code>::first-line</code> are
inherited by <code>::first-letter</code>, but are overridden if the same property is
set on <code>::first-letter</code>.</p></div>
<h4><a name="UIfragments">7.3 The UI element fragments pseudo-elements</a></h4>
<h5><a name="selection">The ::selection pseudo-element</a></h5>
<p>The <code>::selection</code> pseudo-element applies to the portion of a document
that has been highlighted by the user. This also applies, for example, to
selected text within an editable text field. This
pseudo-element should not be confused with the <code><a href="#checked">:checked</a></code>
pseudo-class (which used to be named <code>:selected</code>)
</p><p>Although the <code>::selection</code> pseudo-element is dynamic in nature,
  and is altered by user action, it is reasonable to expect that when a UA rerenders
  to a static medium (such as a printed page, see <a href="#CSS2">[CSS2]</a>)
  which was originally rendered to a dynamic medium (like screen), the UA may
  wish to transfer the current <code>::selection</code> state to that other medium,
  and have all the appropriate formatting and rendering take effect as well. This
  is not required - UAs may omit the <code>::selection</code> pseudo-element for
  static media.
</p><p>These are the CSS properties that apply to <code>::selection</code>
pseudo-elements: color, cursor, background, outline. The computed value of the 'background-image' property on
<code>::selection</code> may be ignored.
</p><h4><a name="gen-content">7.4 The ::before and ::after pseudo-elements</a></h4>
<p>The <code>::before</code> and <code>::after</code> pseudo-elements can be used to
describe generated content before or after an element's content. They are
explained in the Generated Content/Markers CSS3 Module.
</p><p>When the <code>::first-letter</code> and <code>::first-line</code> pseudo-elements
are combined with <code>::before</code> and <code>::after</code>, they apply to the
first letter or line of the element including the inserted text. 
</p><h2><a name="combinators">8. Combinators</a></h2>
<h3><a name="descendant-combinators">8.1 Descendant combinator</a></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 <a href="#whitespace">white space</a> that separates two sequences of simple 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>. 
</p><div class="example">Examples:
  <p>For example, consider the following selector: </p><pre>h1 em</pre>
  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:
  <pre>&lt;h1&gt;This &lt;span class="myclass"&gt;headline&nbsp;
is &lt;em&gt;very&lt;/em&gt; important&lt;/span&gt;&lt;/h1&gt;</pre>The
following selector: <pre>div * p</pre>represents a <code>p</code> element that is a grandchild or later
descendant of a <code>div</code> element. Note the white space on either side of the
"*".
<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><a name="child-combinators">8.2 Child combinators</a></h3>
<p>A&nbsp;<dfn>child combinator</dfn> describes a childhood relationship between
  two elements. A child combinator is made of the "greater-than sign"
  (<code>&gt;</code>) character and separates two sequences of simple selectors.

</p><div class="example">Examples:
  <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>
<p>It represents a <code>p</code> element that is a descendant of an <code>li</code>;
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><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. </p></div>
<h3><a name="adjacent-combinators">8.3 Adjacent sibling combinators</a></h3>
<p>There are two different adjacent sibling combinators: direct adjacent
combinator and indirect adjacent combinator. 
</p><h4><a name="adjacent-d-combinators">8.3.1 Direct adjacent combinators</a></h4>
<p>Direct adjacent combinators are made of the "plus sign" (<code>+</code>)
  character that separates two sequences of simple selectors. The elements represented
  by the two sequences share the same parent in the document tree and the element
  represented by the first sequence immediately precedes the element represented
  by the second one. 
</p><div class="example">Examples:
  <p>Thus, 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. Thus, it adds a constraint
to the <code>h1</code> element that must have <code>class="opener"</code>: </p><pre>h1.opener + h2</pre></div>
<h4><a name="adjacent-i-combinators">8.3.2 Indirect adjacent combinator</a></h4>
<p>Indirect adjacent combinators are made of the "tilde" (<code>~</code>)
  character that separates two sequences of simple selectors. The elements represented
  by the two sequences share the same parent in the document tree and the element
  represented by the first sequence precedes (not necessarily immediately) the
  element represented by the second one. 
</p><div class="example">Example:
  <pre>h1 ~ pre</pre>represents a <code>pre</code> element following an <code>h1</code>. It
is a correct and valid, but partial, description of: <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>
<h2><a name="specificity">9. Calculating a selector's specificity</a></h2>
<p>A selector's specificity is calculated as follows:
</p><ul>
  <li>negative selectors are counted like their simple selectors argument
  </li><li>count the number of ID attributes in the selector (= a)
  </li><li>count the number of other attributes and pseudo-classes in the selector (=
  b)
  </li><li>count the number of element names in the selector (= c)
  </li><li>ignore pseudo-elements. </li></ul>
<p>Concatenating the three numbers a-b-c (in a number system with a large base)
gives the specificity.
</p><div class="example">
  <p>Some 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>
<p><b>Note</b>: the specificity of the styles specified in a HTML
<code>style</code> attribute is described in another CSS3 Module "Cascade and
Inheritance".</p></div>
<div class="html-example"></div>
<h2><a name="w3cselgrammar">10. The grammar of <span class="modulename">Selectors</span></a></h2>
<h3><a name="grammar">10.1 Grammar</a></h3>
<p>The grammar below defines the syntax of <span class="modulename">Selectors</span>.
  It is globally LL(1)  and can be locally LL(2) (but note that most UA's 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&nbsp;<span class="normref"><a class="noxref" href="#yacc" rel="biblioentry">[YACC]</a></span>) are used: 
</p><ul>
  <li><b>*</b>: 0 or more
  </li><li><b>+</b>: 1 or more
  </li><li><b>?</b>: 0 or 1
  </li><li><b>|</b>: separates alternatives
  </li><li><b>[ ]</b>: grouping </li></ul>
<p>The productions are: 
</p><pre>selectors_group
  : selector [ ',' S* selector ]*
  ;

selector
  /* there is at least one sequence of simple selectors in a */
  /* selector and the pseudo-elements occur only in the last */
  /* sequence ; only pseudo-element may occur */
  : [ simple_selector_sequence combinator ]*
       simple_selector_sequence [ pseudo_element ]?
  ;

combinator
  /* combinators can be surrounded by white space */
  : S* [ '+' | '&gt;' | '~' | /* empty */ ] S*
  ;

simple_selector_sequence
  /* the universal selector is optional */
  : [ type_selector | universal ]?
        [ HASH | class | attrib | pseudo_class | negation ]+ |
    type_selector | universal
  ;

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_class
  /* a pseudo-class is an ident, or a function taking an */
  /* ident or a string or a number or a simple selector  */
  /* (excluding negation and pseudo-elements) */
  /* or a an+b expression for argument */
  : ':' [ IDENT | functional_pseudo ]
  ;

functional_pseudo
  : FUNCTION S* [ IDENT | STRING | NUMBER |
                  expression | negation_arg ] S* ')'
  ;

expression
  :  [ [ '-' | INTEGER ]? 'n' [ SIGNED_INTEGER ]? ] | INTEGER
  ;

negation_arg
  : type_selector | universal | HASH | class | attrib | pseudo_class
  ;

pseudo_element
  : [ ':' ]? ':' IDENT
  ;
</pre>
<h3><a name="lex">10.2 Lexical scanner</a></h3>
<p>The following is the&nbsp;<a name="x3"></a><span class="index-def" title="tokenizer">tokenizer</span>, written in Flex (see&nbsp;<span class="normref"><a class="noxref" href="#flex" rel="biblioentry">[FLEX]</a></span>) notation. The tokenizer is case-insensitive.

</p><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&nbsp;<a name="x4"></a><span class="index-inst" title="unicode">Unicode</span>/<a name="x5"></a><span class="index-inst" title="iso-10646">ISO-10646</span>. </p><pre>%option case-insensitive

h&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [0-9a-f]
nonascii&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [\200-\377]
unicode&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\\{h}{1,6}[ \t\r\n\f]?
escape&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {unicode}|\\[ -~\200-\377]
nmstart&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [a-z_]|{nonascii}|{escape}
nmchar&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [a-z0-9-_]|{nonascii}|{escape}
string1&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; \"([\t !#$%&amp;(-~]|\\{nl}|\'|{nonascii}|{escape})*\"
string2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; \'([\t !#$%&amp;(-~]|\\{nl}|\"|{nonascii}|{escape})*\'

ident&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {nmstart}{nmchar}*
name&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {nmchar}+
integer                 [-]?[0-9]+
signed_integer          [-+][0-9]+
num&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {integer}|[0-9]*"."[0-9]+
string&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {string1}|{string2}
nl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; \n|\r\n|\r|\f
%%

[ \t\r\n\f]+&nbsp;&nbsp;&nbsp; {return S;}

\/\*[^*]*\*+([^/][^*]*\*+)*\/&nbsp;&nbsp; /* ignore comments */

"~="&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {return INCLUDES;}
"|="&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {return DASHMATCH;}
"^="&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(return PREFIXMATCH;)
"$="&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(return SUFFIXMATCH;)
"*="&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(return SUBSTRINGMATCH;)
{string}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{return STRING;}
{ident}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {return IDENT;}
{ident}"("&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{return FUNCTION;}
{num}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{return NUMBER;}
{signed_integer}        {return SIGNED_INTEGER;}
{integer]               {return INTEGER;}
"#"{name}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{return HASH;}

.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{return *yytext;}</pre>
<h2><a name="downlevel">11. Namespaces and Down-Level Clients</a></h2>
<p>An important issue is the interaction of CSS selectors with XML documents in
web clients that were produced prior to this document. Unfortunately, due to the
fact that namespaces must be matched based on the URI which identifies the
namespace, not the namespace prefix, some mechanism is required to identify
namespaces in CSS by their URI as well. Without such a mechanism, it is
impossible to construct a CSS style sheet which will properly match selectors in
all cases against a random set of XML documents. However, given complete
knowledge of the XML document to which a style sheet is to be applied, and a
limited use of namespaces within the XML document, it is possible to construct a
style sheet in which selectors would match elements and attributes correctly.

</p><p>It should be noted that a down-level CSS client will (if it properly conforms
to CSS forward compatible parsing rules) ignore all <code>@namespace</code>
at-rules, as well as all style rules that make use of namespace qualified
element type or attribute selectors. The syntax of delimiting namespace prefixes
in CSS was deliberately chosen so that down-level CSS clients would ignore the
style rules rather than possibly match them incorrectly. 
</p><p>The use of default namespaces in CSS makes it possible to write element type
selectors that will function in both namespace aware CSS clients as well as
down-level clients. It should be noted that down-level clients may incorrectly
match selectors against XML elements in other namespaces. 
</p><p>The following are scenarios and examples in which it is possible to construct
style sheets which would function properly in web clients that do not implement
this proposal. 
</p><ol>
  <li>The XML document does not use namespaces.
  <ul>
    <li>In this case, it is obviously not necessary to declare or use namespaces
    in the style sheet. Standard CSS element type and attribute selectors will
    function adequately in a down-level client.
    </li><li>In a CSS namespace aware client, the default behavior of element
    selectors matching without regard to namespace will function properly
    against all elements, since no namespaces are present. However, the use of
    specific element type selectors that match only elements that have no
    namespace ("<code>|name</code>") will guarantee that selectors will match only
    XML elements that do not have a declared namespace. </li></ul>
  </li><li>The XML document defines a single, default namespace used throughout the
  document. No namespace prefixes are used in element names.
  <ul>
    <li>In this case, a down-level client will function as if namespaces were
    not used in the XML document at all. Standard CSS element type and attribute
    selectors will match against all elements. </li></ul>
  </li><li>The XML document does <b>not</b> use a default namespace, all namespace
    prefixes used are known to the style sheet author and there is a direct mapping
    between namespace prefixes and namespace URIs. (A given prefix may only be
    mapped to one namespace URI throughout the XML document, there may be multiple
    prefixes mapped to the same URI).
    <ul>
    <li>In this case, the down-level client will view and match element type and
    attribute selectors based on their fully qualified name, not the local part
    as outlined in the <a href="#typenmsp">Type selectors and
    Namespaces</a> section. CSS selectors may be declared using an escaped colon
    "<code>\:</code>" to describe the fully qualified names, e.g.
    "<code>html\:h1</code>" will match <code>&lt;html:h1&gt;</code>. Selectors using the
    qualified name will only match XML elements that use the same prefix. Other
    namespace prefixes used in the XML that are mapped to the same URI will not
    match as expected unless additional CSS style rules are declared for them.
    </li><li>Note that selectors declared in this fashion will <i>only</i> match in
    down-level clients. A CSS namespace aware client will match element type and
    attribute selectors based on the name's local part. So selectors declared
    with the fully qualified name will not match (unless there is no namespace
    prefix in the fully qualified name). </li></ul></li></ol>
<p>In other scenarios: when the namespace prefixes used in the XML are not known
in advance by the style sheet author; or a combination of elements with no
namespace are used in conjunction with elements using a default namespace; or
the same namespace prefix is mapped to <i>different</i> namespace URIs within
the same document, or in different documents; it is impossible to construct a
CSS style sheet that will function properly against all elements in those
documents, unless, the style sheet is written using a namespace URI syntax (as
outlined in this document or similar) and the document is processed by a CSS and
XML namespace aware client. 
</p><h2><a name="profiling">12. Profiles</a></h2>
<p>Each specification using <span class="modulename">Selectors</span> must define the subset of W3C
Selectors it allows and excludes, and describe the local meaning of all the
components of that subset.
</p><p>Non normative examples:
</p><div class="profile">
<table class="tprofile" width="75%" border="1">
  <tbody>
  <tr>
    <th class="title" colspan="2"><span class="modulename">Selectors</span> profile</th></tr>
  <tr>
    <th>Specification</th>
    <td>CSS level 1</td></tr>
  <tr>
    <th>Accepts</th>
    <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&nbsp;</td></tr>
  <tr>
    <th>Excludes</th>
    <td>
      <p>universal selector<br>attribute selectors<br>:hover and :focus
      pseudo-classes<br>:target pseudo-class<br>:lang() pseudo-class<br>all UI
      element states pseudo-classes<br>all structural
      pseudo-classes<br>:contains() pseudo-class<br>negation pseudo-class<br>all
      UI element fragments pseudo-elements<br>::before and ::after
      pseudo-elements<br>child combinators<br>adjacent sibling combinators
      </p><p>namespaces</p></td></tr>
  <tr>
    <th>Extra constraints</th>
    <td>only one class selector allowed per sequence of simple
  selectors</td></tr></tbody></table><br>&nbsp; <br>&nbsp;
<table class="tprofile" width="75%" border="1">
  <tbody>
  <tr>
    <th class="title" colspan="2"><span class="modulename">Selectors</span> profile</th></tr>
  <tr>
    <th>Specification</th>
    <td>CSS level 2</td></tr>
  <tr>
    <th>Accepts</th>
    <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 direct
      combinator <br>::first-line and ::first-letter pseudo-elements<br>::before
      and ::after pseudo-elements</td></tr>
  <tr>
    <th>Excludes</th>
    <td>
      <p>content selectors <br>substring matching attribute selectors<br>:target
      pseudo-classes&nbsp; <br>all UI element states pseudo-classes<br>all
      structural pseudo-classes other than :first-child<br>:contains()
      pseudo-class<br>negation pseudo-class<br>all UI element fragments
      pseudo-elements<br>adjacent indirect combinators 
      </p><p>namespaces</p></td></tr>
  <tr>
    <th>Extra constraints</th>
    <td>more than one class selector per sequence of simple selectors (CSS1
      constraint) allowed</td></tr></tbody></table>
<p>In CSS, selectors express pattern matching rules that determine which style
rules apply to elements in the document tree. 
</p><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>: </p><pre>h1 a[name]</pre>
<p>All CSS declarations attached to such a selector are applied to elements
matching it. </p></div>
<div class="profile">
<table class="tprofile" width="75%" border="1">
  <tbody>
  <tr>
    <th class="title" colspan="2"><span class="modulename">Selectors</span> profile</th></tr>
  <tr>
    <th>Specification</th>
      <td>STTS 3</td>
    </tr>
  <tr>
    <th>Accepts</th>
    <td>
      <p>type selectors<br>universal selectors<br>attribute selectors<br>class
      selectors<br>ID selectors<br>all structural pseudo-classes<br>
          :contains() pseudo-class<br>
          all combinators
      </p><p>namespaces</p></td></tr>
  <tr>
    <th>Excludes</th>
    <td>non accepted pseudo-classes<br>pseudo-elements<br></td></tr>
  <tr>
    <th>Extra constraints</th>
    <td>some selectors and combinators are not allowed in fragment
      descriptions on the right side of STTS declarations.</td></tr></tbody></table>
  <p><span class="modulename">Selectors</span> can be used in STTS 3 in two different
    manners: 
</p><ol>
  <li>a selection mechanism equivalent to CSS selection mechanism: declarations
  attached to a given selector are applied to elements matching that selector,
  </li><li>fragment descriptions that appear on the right side of declarations.
</li></ol></div>
<h2><a name="Conformance"></a>13. Conformance and Requirements</h2>
<p>This section defines conformance with the present specification only.
</p><p>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><p>All specifications reusing <span class="modulename">Selectors</span> must contain a <a href="#profiling">Profile</a> listing the
subset of <span class="modulename">Selectors</span> it accepts or excludes, and describing the constraints
it adds to the current specification. 
</p><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><p>User agents must observe the rules for handling parsing errors:
</p><ul>
  <li>a simple selector containing an undeclared namespace prefix is invalid</li>
  <li>a selector containing an invalid simple selector, an invalid combinator
    or an invalid token is invalid. </li>
  <li>a group of selectors containing an invalid selector is invalid.</li>
</ul>
<p>Implementations of this specification must behave as "recipients
of text data" as defined by
<a class="noxref" href="#CWWW" rel="biblioentry"><span class="normref">[CWWW]</span></a>
when parsing selectors and attempting matches. (In particular, implementations must assume
the data is normalized and must not normalize it.) Normative rules
for matching strings are defined in
<a class="noxref" href="#CWWW" rel="biblioentry"><span class="normref">[CWWW]</span></a>
and <a class="noxref" href="#UNICODE" rel="biblioentry"><span class="normref">[UNICODE]</span></a>
and apply to implementations of this specification.

</p><h2><a name="Tests"></a>14. Tests</h2>
<p>This specification contains a test suite 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 <span class="propernoun">Selectors</span>.
</p><p>These tests are available [link forthcoming].
</p><h2><a name="ACKS"></a>15. Acknowledgements</h2>
<p>This specification is the product of the W3C Working Group on Cascading Style
Sheets and Formatting Properties. In addition to the editors of this
specification, the members of the Working Group are:
</p><ul>
  <li>Marc Attinasi (Netscape/AOL)
  </li><li>Bert Bos (W3C)
  </li><li>Tantek Çelik (Microsoft Corp.)
  </li><li>Don Day (IBM)
  </li><li>Martin Dürst (W3C)
  </li><li>Angel Diaz (IBM)
  </li><li>Daniel Glazman (Netscape/AOL from November 2000, and Electricité de France
    until February 2000)
  </li><li>Håkon W. Lie (Opera Software from April 1999, and W3C until April 1999)
  </li><li>Chris Lilley (W3C)
  </li><li>Dave Raggett (W3C/Openwave Systems Inc.)
  </li><li>Pierre Saslawsky (Netscape/AOL)
  </li><li>Robert Stevahn (Hewlett-Packard)
  </li><li>Michel Suignard (Microsoft Corp.)
  </li><li>Ted Wugofski (Openwave Systems Inc.)
  </li><li>Steve Zilles (Adobe) </li></ul>
<p>A number of invited experts to the Working Group have significantly contributed
  to CSS3: L. David Baron, Tim Boland (NIST), Todd Fahrner, Daniel Glazman, Ian
  Hickson, Eric Meyer (The OPAL Group), Jeff Veen.
</p><p>Former members of the Working Group:
</p><ul>
  <li>Chris Brichford (Adobe)
  </li><li>Troy Chevalier (Netscape/AOL)
  </li><li>Dwayne Dicks (SoftQuad)
  </li><li>Ian Jacobs (W3C)
  </li><li>Lorin Jurow (Quark)
  </li><li>Sho Kuwamoto (Macromedia)
  </li><li>Peter Linss (Netscape/AOL)
  </li><li>Steven Pemberton (CWI)
  </li><li>Robert Pernett (Lotus)
  </li><li>Douglas Rand (SGI)
  </li><li>Nisheeth Ranjan (Netscape/AOL)
  </li><li>Ed Tecot (Microsoft Corp.)
  </li><li>Jared Sorensen (Novell)
  </li><li>Mike Wexler (Adobe)
  </li><li>John Williams (Quark)
  </li><li>Chris Wilson (Microsoft Corp.) </li></ul>
<p>We thank all of them (members, invited experts and former members) for their
efforts.
</p><p>Of course, this document derives from the CSS Level 1 and CSS level 2
Recommendations. We thank all CSS1 and CSS2 authors, editors and
contributors.
</p><p>Dr. Hasan Ali Çelik suggested the simple and powerful syntax of the argument
for :nth-child() while the Working Group was considering much more complex
solutions.
</p><p>The discussions on www-style@w3.org have been influential in many key issues.
  Especially, we would like to thank Ian Graham, David Baron, Björn Höhrmann,
  <i>fantasai</i>, Jelks Cabanis and Matthew Brealey for their active and useful
  participation.
</p><h2><a name="references">16. References</a></h2>
<ol class="refs">
  <li>[CSS1] <a name="CSS1"></a>Bert Bos, Håkon Wium Lie; "<i>Cascading Style
    Sheets, level 1</i>", W3C Recommendation, 17 Dec 1996, revised 11 Jan 1999<br>
    (<code><a href="http://www.w3.org/TR/REC-CSS1">http://www.w3.org/TR/REC-CSS1</a></code>)
  </li><li>[CSS2]<a name="CSS2"></a> Bert Bos, Håkon Wium Lie, Chris Lilley, Ian
    Jacobs, editors; "<i>Cascading Style Sheets, level 2</i>", W3C Recommendation,
    12 May 1998 <br>
    (<code><a href="http://www.w3.org/TR/REC-CSS2/">http://www.w3.org/TR/REC-CSS2/</a></code>)
  </li><li id="CWWW">[CWWW] Martin J. Dürst, François Yergeau, Misha Wolf,
    Asmus Freytag, Tex Texin, editors; "<i>Character Model for the World Wide
    Web</i>", W3C Working Draft, 26 January 2001<br>
    (<code><a href="http://www.w3.org/TR/2001/WD-charmod-20010126">http://www.w3.org/TR/2001/WD-charmod-20010126</a></code>)
  </li><li>[FLEX] <a name="flex"></a>"Flex: The Lexical Scanner Generator",
    Version 2.3.7, ISBN 1882114213</li>
  <li>[HTML4.01] <a name="html40"></a>Dave Ragget, Arnaud Le Hors, Ian Jacobs,
    editors; "HTML 4.01 Specification", W3C Recommendation, 24 December
    1999<br>
    (<a href="http://www.w3.org/TR/html401/"><code>http://www.w3.org/TR/html401/</code></a>)</li>
  <li>[MATH] <a name="MATH"></a>Patrick Ion, Robert Miner; "<i>Mathematical
    Markup Language (MathML) 1.01</i>", W3C Recommendation, revision of 7
    July 1999<br>
    (<code><a href="http://www.w3.org/1999/07/REC-MathML-19990707">http://www.w3.org/1999/07/REC-MathML-19990707</a></code>)<br>
  </li>
  <li>[NMSP]&nbsp;<a name="nmsp19990625"></a>Peter Linss, editor; "<i>CSS Namespace
    Enhancements (Proposal)</i>", W3C Working Draft, 25 June 1999 <br>
    (<code><a href="http://www.w3.org/1999/06/25/WD-css3-namespace-19990625/">http://www.w3.org/1999/06/25/WD-css3-namespace-19990625/</a></code>)
  </li>
  <li>[RFC3066] <a name="rfc3066"></a>H. Alvestrand; "Tags for the Identification
    of Languages", Request for Comments 3066, January 2001<br>
    (<a href="http://www.ietf.org/rfc/rfc3066.txt"><code>http://www.ietf.org/rfc/rfc3066.txt</code></a>)
  </li>
  <li>[STTS3]<a name="STTS"></a> Daniel Glazman ; "<i>Simple Tree Transformation
    Sheets 3</i>", Electricité de France, submission to the W3C, 11 Nov
    1998 <br>
    (<code><a href="http://www.w3.org/TR/NOTE-STTS3">http://www.w3.org/TR/NOTE-STTS3</a></code>)
  </li><li>[SVG] <a name="SVG"></a>Jon Ferraiolo ed.; "<i>Scalable Vector Graphics
    (SVG) 1.0 Specification</i>", W3C Proposed Recommendation, 19 July 2001<br>
    (<code><a href="http://www.w3.org/TR/2001/PR-SVG-20010719">http://www.w3.org/TR/2001/PR-SVG-20010719</a></code>)<br>
  </li><li>[UI]&nbsp;<a name="UI-WD"></a>Tantek Çelik, editor; "<i>User Interface
    for CSS3</i>", W3C Working Draft, 16 February 2000 <br>
    (<code><a href="http://www.w3.org/TR/2000/WD-css3-userint-20000216">http://www.w3.org/TR/2000/WD-css3-userint-20000216</a></code>)
  </li><li>[UNICODE] <a name="UNICODE"></a>"<i>The Unicode Standard: Version 3.0.1</i>",
    The Unicode Consortium, Addison Wesley Longman, 2000, ISBN 0-201-61633-5.<br>
    URL: <a href="http://www.unicode.org/unicode/standard/versions/Unicode3.0.1.html">http://www.unicode.org/unicode/standard/versions/Unicode3.0.1.html</a>.<br>
    The latest version of Unicode. For more information, consult the Unicode Consortium's
    home page at <code><a href="http://www.unicode.org/">http://www.unicode.org/</a></code>.
  </li><li>[XML-NAMES] <a name="XMLNAMES"></a>Tim Bray, Dave Hollander, Andrew Layman,
    editors; "Namespaces in XML", W3C Recommendation, 14 January 1999<br>
    (<a href="http://www.w3.org/TR/REC-xml-names/"><code>http://www.w3.org/TR/REC-xml-names/</code></a>)</li>
  <li>[YACC] <a name="yacc"></a>"YACC - Yet another compiler compiler",
    S. C. Johnson, Technical Report, Murray Hill, 1975</li>
</ol>
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