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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" debug="true">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<script src="http://www.google.com/jsapi"></script>
<script src="config/frameworks.js" type="text/javascript"></script>
<script src="system/runtime.js" type="text/javascript"></script>
</head>
<body>
<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>
<h1 id="title">Selectors</h1>
<h2>W3C Working Draft 15 December 2005</h2>
<dl>
<dt>This version:
<dd><a href="http://www.w3.org/TR/2005/WD-css3-selectors-20051215">
http://www.w3.org/TR/2005/WD-css3-selectors-20051215</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css3-selectors">
http://www.w3.org/TR/css3-selectors</a>
<dt>Previous version:
<dd><a href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113">
http://www.w3.org/TR/2001/CR-css3-selectors-20011113</a>
<dt><a name=editors-list></a>Editors:
<dd class="vcard"><span class="fn">Daniel Glazman</span> (Invited Expert)</dd>
<dd class="vcard"><a lang="tr" class="url fn" href="http://www.tantek.com/">Tantek Çelik</a> (Invited Expert)
<dd class="vcard"><a href="mailto:ian@hixie.ch" class="url fn">Ian Hickson</a> (<span
class="company"><a href="http://www.google.com/">Google</a></span>)
<dd class="vcard"><span class="fn">Peter Linss</span> (former editor, <span class="company"><a
href="http://www.netscape.com/">Netscape/AOL</a></span>)
<dd class="vcard"><span class="fn">John Williams</span> (former editor, <span class="company"><a
href="http://www.quark.com/">Quark, Inc.</a></span>)
</dl>
<p class="copyright"><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">
Copyright</a> © 2005 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts
Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.org/"><acronym title="European Research
Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a
href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>,
<a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.
<hr title="Separator for header">
</div>
<h2><a name=abstract></a>Abstract</h2>
<p><em>Selectors</em> are patterns that match against elements in a
tree. Selectors have been optimized for use with HTML and XML, and
are designed to be usable in performance-critical code.</p>
<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. CSS uses Selectors for binding
style properties to elements in the document. This document
describes extensions to the selectors defined in CSS level 2. These
extended selectors will be used by CSS level 3.
<p>Selectors define the following function:</p>
<pre>expression ∗ element → boolean</pre>
<p>That is, given an element and a selector, this specification
defines whether that element matches the selector.</p>
<p>These expressions can also be used, for instance, to select a set
of elements, or a single element from a set of elements, by
evaluating the expression across all the elements in a
subtree. <acronym title="Simple Tree Transformation
Sheets">STTS</acronym> (Simple Tree Transformation Sheets), a
language for transforming XML trees, uses this mechanism. <a href="#refsSTTS">[STTS]</a></p>
<h2><a name=status></a>Status of this document</h2>
<p><em>This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest revision
of this technical report can be found in the <a
href="http://www.w3.org/TR/">W3C technical reports index at
http://www.w3.org/TR/.</a></em></p>
<p>This document describes the selectors that already exist in <a
href="#refsCSS1"><abbr title="CSS level 1">CSS1</abbr></a> and <a
href="#refsCSS21"><abbr title="CSS level 2">CSS2</abbr></a>, and
also proposes new selectors for <abbr title="CSS level
3">CSS3</abbr> and other languages that may need them.</p>
<p>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, called profiles. For
example, it may be that only a profile for interactive user agents
will include all of the selectors.</p>
<p>This specification is a last call working draft for the the <a
href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>
(<a href="/Style/">Style Activity</a>). This
document is a revision of the <a
href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113/">Candidate
Recommendation dated 2001 November 13</a>, and has incorporated
implementation feedback received in the past few years. It is
expected that this last call will proceed straight to Proposed
Recommendation stage since it is believed that interoperability will
be demonstrable.</p>
<p>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.
The deadline for comments is 14 January 2006.</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 Working Draft as other than "work in progress".
<p>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.
<div class="subtoc">
<h2><a name=contents>Table of contents</a></h2>
<ul class="toc">
<li class="tocline2"><a href="#context">1. Introduction</a>
<ul>
<li><a href="#dependencies">1.1. Dependencies</a> </li>
<li><a href="#terminology">1.2. Terminology</a> </li>
<li><a href="#changesFromCSS2">1.3. Changes from CSS2</a> </li>
</ul>
<li class="tocline2"><a href="#selectors">2. Selectors</a>
<li class="tocline2"><a href="#casesens">3. Case sensitivity</a>
<li class="tocline2"><a href="#selector-syntax">4. Selector syntax</a>
<li class="tocline2"><a href="#grouping">5. Groups of selectors</a>
<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 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 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><a href="#attribute-substrings">6.3.2. Substring matching attribute selectors</a>
<li class="tocline4"><a href="#attrnmsp">6.3.3. Attribute selectors and namespaces</a>
<li class="tocline4"><a href="#def-values">6.3.4. Default attribute values in DTDs</a></li>
</ul>
<li class="tocline3"><a href="#class-html">6.4. Class selectors</a>
<li class="tocline3"><a href="#id-selectors">6.5. ID selectors</a>
<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 class="tocline4"><a href="#target-pseudo">6.6.2. The :target pseudo-class</a>
<li class="tocline4"><a href="#lang-pseudo">6.6.3. The :lang() pseudo-class</a>
<li class="tocline4"><a href="#UIstates">6.6.4. UI element states pseudo-classes</a>
<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><a href="#nth-child-pseudo">:nth-child() pseudo-class</a>
<li><a href="#nth-last-child-pseudo">:nth-last-child()</a>
<li><a href="#nth-of-type-pseudo">:nth-of-type() pseudo-class</a>
<li><a href="#nth-last-of-type-pseudo">:nth-last-of-type()</a>
<li><a href="#first-child-pseudo">:first-child pseudo-class</a>
<li><a href="#last-child-pseudo">:last-child pseudo-class</a>
<li><a href="#first-of-type-pseudo">:first-of-type pseudo-class</a>
<li><a href="#last-of-type-pseudo">:last-of-type pseudo-class</a>
<li><a href="#only-child-pseudo">:only-child pseudo-class</a>
<li><a href="#only-of-type-pseudo">:only-of-type pseudo-class</a>
<li><a href="#empty-pseudo">:empty pseudo-class</a></li>
</ul>
<li class="tocline4"><a href="#negation">6.6.7. The negation pseudo-class</a></li>
</ul>
</li>
</ul>
<li><a href="#pseudo-elements">7. Pseudo-elements</a>
<ul>
<li><a href="#first-line">7.1. The ::first-line pseudo-element</a>
<li><a href="#first-letter">7.2. The ::first-letter pseudo-element</a>
<li><a href="#UIfragments">7.3. The ::selection pseudo-element</a>
<li><a href="#gen-content">7.4. The ::before and ::after pseudo-elements</a></li>
</ul>
<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 class="tocline3"><a href="#child-combinators">8.2. Child combinators</a>
<li class="tocline3"><a href="#sibling-combinators">8.3. Sibling combinators</a>
<ul class="toc">
<li class="tocline4"><a href="#adjacent-sibling-combinators">8.3.1. Adjacent sibling combinator</a>
<li class="tocline4"><a href="#general-sibling-combinators">8.3.2. General sibling combinator</a></li>
</ul>
</li>
</ul>
<li class="tocline2"><a href="#specificity">9. Calculating a selector's specificity</a>
<li class="tocline2"><a href="#w3cselgrammar">10. The grammar of Selectors</a>
<ul class="toc">
<li class="tocline3"><a href="#grammar">10.1. Grammar</a>
<li class="tocline3"><a href="#lex">10.2. Lexical scanner</a></li>
</ul>
<li class="tocline2"><a href="#downlevel">11. Namespaces and down-level clients</a>
<li class="tocline2"><a href="#profiling">12. Profiles</a>
<li><a href="#Conformance">13. Conformance and requirements</a>
<li><a href="#Tests">14. Tests</a>
<li><a href="#ACKS">15. Acknowledgements</a>
<li class="tocline2"><a href="#references">16. References</a>
</ul>
</div>
<h2><a name=context>1. Introduction</a></h2>
<h3><a name=dependencies></a>1.1. Dependencies</h3>
<p>Some features of this specification are specific to CSS, or have
particular limitations or rules specific to CSS. In this
specification, these have been described in terms of CSS2.1. <a
href="#refsCSS21">[CSS21]</a></p>
<h3><a name=terminology></a>1.2. Terminology</h3>
<p>All of the text of this specification is normative except
examples, notes, and sections explicitly marked as
non-normative.</p>
<h3><a name=changesFromCSS2></a>1.3. Changes from CSS2</h3>
<p><em>This section is non-normative.</em></p>
<p>The main differences between the selectors in CSS2 and those in
Selectors are:
<ul>
<li>the list of basic definitions (selector, group of selectors,
simple selector, etc.) has been changed; in particular, what was
referred to in CSS2 as a simple selector is now called a sequence
of simple selectors, and the term "simple selector" is now used for
the components of this sequence</li>
<li>an optional namespace component is now allowed in type element
selectors, the universal selector and attribute selectors</li>
<li>a <a href="#general-sibling-combinators">new combinator</a> has been introduced</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>the grammar has been rewritten</li>
<li>profiles to be added to specifications integrating Selectors
and defining the set of selectors which is actually supported by
each specification</li>
<li>Selectors 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 has its own test suite</li>
</ul>
<h2><a name=selectors></a>2. Selectors</h2>
<p><em>This section is non-normative, as it merely summarizes the
following sections.</em></p>
<p>A Selector represents a structure. This structure can be used as a
condition (e.g. in a CSS rule) that determines which elements a
selector matches in the document tree, or as a flat description of the
HTML or XML fragment corresponding to that structure.</p>
<p>Selectors may range from simple element names to rich contextual
representations.</p>
<p>The following table summarizes the Selector syntax:</p>
<table class="selectorsReview">
<thead>
<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>
<tbody>
<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</a></td>
<td class="origin">2</td></tr>
<tr>
<td class="pattern">E:enabled<br>E:disabled</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--></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::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 > 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-sibling-combinators">Adjacent sibling 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="#general-sibling-combinators">General sibling 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 in the "Meaning"
column.</p>
<h2><a name=casesens>3. Case sensitivity</a></h2>
<p>The case sensitivity of document language element names, attribute
names, and attribute values in selectors depends on the document
language. For example, in HTML, element names are case-insensitive,
but in XML, they are case-sensitive.</p>
<h2><a name=selector-syntax>4. Selector syntax</a></h2>
<p>A <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 <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 <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="#class-html">class 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" (U+003E, <code>></code>), "plus sign" (U+002B,
<code>+</code>) and "tilde" (U+007E, <code>~</code>). White
space may appear between a combinator and the simple selectors around
it. <a name=whitespace></a>Only the characters "space" (U+0020), "tab"
(U+0009), "line feed" (U+000A), "carriage return" (U+000D), and "form
feed" (U+000C) can occur in white space. Other space-like characters,
such as "em-space" (U+2003) and "ideographic space" (U+3000), are
never part of white space.</p>
<p>The elements of a document tree that are represented by a selector
are the <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 last sequence of
simple selectors.</p>
<p>An empty selector, containing no sequence of simple selectors and
no pseudo-element, is an <a href="#Conformance">invalid
selector</a>.</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. (A comma is U+002C.)</p>
<div class="example">
<p>CSS examples:</p>
<p>In this example, we condense three rules with identical
declarations into one. Thus,</p>
<pre>h1 { font-family: sans-serif }
h2 { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is equivalent to:</p>
<pre>h1, h2, h3 { font-family: sans-serif }</pre>
</div>
<p><strong>Warning</strong>: the equivalence is true in this example
because all the selectors are valid selectors. If just one of these
selectors were invalid, the entire group of selectors would be
invalid. This would invalidate the rule for all three heading
elements, whereas in the former case only one of the three individual
heading rules would be invalidated.</p>
<h2><a name=simple-selectors>6. Simple selectors</a></h2>
<h3><a name=type-selectors>6.1. Type selector</a></h3>
<p>A <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">
<p>Example:</p>
<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="#refsXMLNAMES">[XMLNAMES]</a>) component. A namespace prefix
that has been previously declared may be prepended to the element name
separated by the namespace separator "vertical bar"
(U+007C, <code>|</code>).</p>
<p>The namespace component may be left empty to indicate that the
selector is only to represent elements with no declared namespace.</p>
<p>An asterisk may be used for the namespace prefix, indicating that
the selector represents elements in any namespace (including elements
with no namespace).</p>
<p>Element type selectors that have no namespace component (no
namespace separator), represent elements without regard to the
element's namespace (equivalent to "<code>*|</code>") unless a default
namespace has been declared. If a default namespace has been declared,
the selector will represent only elements in the default
namespace.</p>
<p>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 Selectors. In CSS, such a mechanism is defined
in the General Syntax module.</p>
<p>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 <dfn>universal selector</dfn>, written "asterisk"
(<code>*</code>), represents the qualified name of any element
type. It represents 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.</p>
<div class="example">
<p>Examples:</p>
<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 class="note"><strong>Note:</strong> 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. It
is used as follows:</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>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 Selectors. 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>Selectors allow the representation of an element's attributes. When
a selector is used as an expression to match against an element,
attribute selectors must be considered to match an element if that
element has an attribute that matches the attribute represented by the
attribute selector.</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>
<dd>Represents an element with the <code>att</code> attribute, whatever the value of
the attribute.</dd>
<dt><code>[att=val]</code></dt>
<dd>Represents an element with the <code>att</code> attribute whose value is exactly
"val".</dd>
<dt><code>[att~=val]</code></dt>
<dd>Represents an element with the <code>att</code> attribute whose value is a <a
href="#whitespace">whitespace</a>-separated list of words, one of
which is exactly "val". If "val" contains whitespace, it will never
represent anything (since the words are <em>separated</em> by
spaces).</dd>
<dt><code>[att|=val]</code>
<dd>Represents an element with the <code>att</code> attribute, its value either
being exactly "val" or beginning with "val" immediately followed by
"-" (U+002D). This is primarily intended to allow language subcode
matches (e.g., the <code>hreflang</code> attribute on the
<code>link</code> element in HTML) as described in RFC 3066 (<a
href="#refsRFC3066">[RFC3066]</a>). 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">
<p>Examples:</p>
<p>The following attribute selector represents an <code>h1</code>
element that carries the <code>title</code> attribute, whatever its
value:</p>
<pre>h1[title]</pre>
<p>In the following example, the selector represents a
<code>span</code> element whose <code>class</code> attribute has
exactly the value "example":</p>
<pre>span[class="example"]</pre>
<p>Multiple attribute selectors can be used to represent several
attributes of an element, or several conditions on the same
attribute. Here, the selector represents a <code>span</code> element
whose <code>hello</code> attribute has exactly the value "Cleveland"
and whose <code>goodbye</code> attribute has exactly the value
"Columbus":</p>
<pre>span[hello="Cleveland"][goodbye="Columbus"]</pre>
<p>The following 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]
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 an element with the <code>att</code> attribute whose value begins
with the prefix "val".</dd>
<dt><code>[att$=val]</code>
<dd>Represents an element with the <code>att</code> attribute whose value ends with
the suffix "val".</dd>
<dt><code>[att*=val]</code>
<dd>Represents an element with the <code>att</code> attribute whose value contains
at least one instance of the substring "val".</dd>
</dl>
<p>Attribute values must be identifiers or strings. The
case-sensitivity of attribute names in selectors depends on the
document language.</p>
<div class="example">
<p>Examples:</p>
<p>The following selector represents an HTML <code>object</code>, referencing an
image:</p>
<pre>object[type^="image/"]</pre>
<p>The following selector represents an HTML anchor <code>a</code> with an
<code>href</code> attribute whose value ends with ".html".</p>
<pre>a[href$=".html"]</pre>
<p>The following selector represents an HTML paragraph with a <code>title</code>
attribute whose value contains the substring "hello"</p>
<pre>p[title*="hello"]</pre>
</div>
<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>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 Selectors.
In CSS, such a mechanism is defined in the General Syntax module.
<div class="example">
<p>CSS examples:</p>
<pre>@namespace foo "http://www.example.com";
[foo|att=val] { color: blue }
[*|att] { color: yellow }
[|att] { color: green }
[att] { color: green }</pre>
<p>The first rule will match only elements with the attribute
<code>att</code> in the "http://www.example.com" namespace with the
value "val".</p>