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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head>
<title>Selectors Level 3</title>
<link href=default.css rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1 id=title>Selectors Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 17 February
2011</h2>
<dl>
<dt>This version:
<dd> <!-- <a href="http://www.w3.org/TR/2011/ED-selectors3-20110217">
http://www.w3.org/TR/2011/PR-selectors3-20110217</a> -->
<a href="http://dev.w3.org/csswg/selectors3">
http://dev.w3.org/csswg/selectors3</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/2009/PR-css3-selectors-20091215/">
http://www.w3.org/TR/2009/PR-css3-selectors-20091215/</a>
<dt><a name=editors-list></a>Editors:
<dd class=vcard><a class="url fn" href="http://www.tantek.com/"
lang=tr>Tantek Çelik</a> (Invited Expert)
<dd class=vcard><a class="url fn"
href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
(Invited Expert)
<dd class=vcard><span class=fn>Daniel Glazman</span> (Disruptive
Innovations SARL)
<dd class=vcard><a class="url fn" href="mailto:ian@hixie.ch">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>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2011 <a
href="http://www.w3.org/"><acronym title="World Wide Web
Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
title="European Research Consortium for Informatics and
Mathematics">ERCIM</acronym></a>, <a
href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p><em>Selectors</em> are patterns that match against elements in a tree,
and as such form one of several technologies that can be used to select
nodes in an XML document. Selectors have been optimized for use with HTML
and XML, and are designed to be usable in performance-critical code.
<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.
<p>This document describes the selectors that already exist in <abbr
title="CSS level 1">CSS1</abbr> <a href="#CSS1"
rel=biblioentry>[CSS1]<!--{{CSS1}}--></a> and <abbr title="CSS level
2">CSS2</abbr> <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, and further introduces new
selectors for <abbr title="CSS level 3">CSS3</abbr> and other languages
that may need them.
<p>Selectors define the following function:
<pre>expression ∗ element → boolean</pre>
<p>That is, given an element and a selector, this specification defines
whether that element matches the selector.
<p>These expressions can also be used, for instance, to select a set of
elements, or a single element from a set of elements, by evaluating the
expression across all the elements in a subtree. <acronym title="Simple
Tree Transformation Sheets">STTS</acronym> (Simple Tree Transformation
Sheets), a language for transforming XML trees, uses this mechanism. <a
href="#STTS3" rel=biblioentry>[STTS3]<!--{{STTS3}}--></a>
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bselectors3%5D%20PUT%20SUBJECT%20HERE">
www-style@w3.org</a> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
discussion of this specification. When sending e-mail, please put the text
“selectors3” in the subject, preferably like this:
“[<!---->selectors3<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p>A separate <a
href="/Style/CSS/Test/CSS3/Selectors/20091025/reports/CR-ImpReport.html">
implementation report</a> contains a test suite and shows several
implementations of the specification.
<p>The <a href=issues-lc-2009>list of comments on the last draft</a>
explains the changes that were made since that draft.
<p>The bibliography contains <a href="#normative-references">normative
references</a> to two W3C specifications that are not Recommendations at
the time of publication, although they are believed to be stable. It is
currently the intention to keep this specification at Proposed
Recommendation level until those specifications are themselves Proposed
Recommendations or Recommendations.
<p><em>Advisory Committee representatives of W3C member organizations are
requested to fill in the <a href="/2002/09/wbs/33280/css3-selectors-PR/">
review form</a> before 31 January 2010.</em>
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#context"><span class=secno>1. </span>Introduction</a>
<ul class=toc>
<li><a href="#dependencies"><span class=secno>1.1.
</span>Dependencies</a>
<li><a href="#terminology"><span class=secno>1.2. </span>Terminology</a>
<li><a href="#changesFromCSS2"><span class=secno>1.3. </span>Changes
from CSS2</a>
</ul>
<li><a href="#selectors"><span class=secno>2. </span>Selectors</a>
<li><a href="#casesens"><span class=secno>3. </span>Case sensitivity</a>
<li><a href="#selector-syntax"><span class=secno>4. </span>Selector
syntax</a>
<li><a href="#grouping"><span class=secno>5. </span>Groups of
selectors</a>
<li><a href="#simple-selectors"><span class=secno>6. </span>Simple
selectors</a>
<ul class=toc>
<li><a href="#type-selectors"><span class=secno>6.1. </span>Type
selector</a>
<ul class=toc>
<li><a href="#typenmsp"><span class=secno>6.1.1. </span>Type selectors
and namespaces</a>
</ul>
<li><a href="#universal-selector"><span class=secno>6.2.
</span>Universal selector </a>
<ul class=toc>
<li><a href="#univnmsp"><span class=secno>6.2.1. </span>Universal
selector and namespaces</a>
</ul>
<li><a href="#attribute-selectors"><span class=secno>6.3.
</span>Attribute selectors</a>
<ul class=toc>
<li><a href="#attribute-representation"><span class=secno>6.3.1.
</span>Attribute presence and value selectors</a>
<li><a href="#attribute-substrings"><span class=secno>6.3.2.
</span>Substring matching attribute selectors</a>
<li><a href="#attrnmsp"><span class=secno>6.3.3. </span>Attribute
selectors and namespaces</a>
<li><a href="#def-values"><span class=secno>6.3.4. </span>Default
attribute values in DTDs</a>
</ul>
<li><a href="#class-html"><span class=secno>6.4. </span>Class
selectors</a>
<li><a href="#id-selectors"><span class=secno>6.5. </span>ID
selectors</a>
<li><a href="#pseudo-classes"><span class=secno>6.6.
</span>Pseudo-classes</a>
<ul class=toc>
<li><a href="#dynamic-pseudos"><span class=secno>6.6.1. </span>Dynamic
pseudo-classes</a>
<ul class=toc>
<li><a href="#the-link-pseudo-classes-link-and-visited"><span
class=secno>6.6.1.1. </span>The link pseudo-classes: :link and
:visited</a>
<li><a href="#the-user-action-pseudo-classes-hover-act"><span
class=secno>6.6.1.2. </span>The user action pseudo-classes :hover,
:active, and :focus</a>
</ul>
<li><a href="#target-pseudo"><span class=secno>6.6.2. </span>The
target pseudo-class :target</a>
<li><a href="#lang-pseudo"><span class=secno>6.6.3. </span>The
language pseudo-class :lang</a>
<li><a href="#UIstates"><span class=secno>6.6.4. </span>The UI element
states pseudo-classes</a>
<ul class=toc>
<li><a href="#enableddisabled"><span class=secno>6.6.4.1. </span>The
:enabled and :disabled pseudo-classes</a>
<li><a href="#checked"><span class=secno>6.6.4.2. </span>The
:checked pseudo-class</a>
<li><a href="#indeterminate"><span class=secno>6.6.4.3. </span>The
:indeterminate pseudo-class</a>
</ul>
<li><a href="#structural-pseudos"><span class=secno>6.6.5.
</span>Structural pseudo-classes</a>
<ul class=toc>
<li><a href="#root-pseudo"><span class=secno>6.6.5.1. </span>:root
pseudo-class</a>
<li><a href="#nth-child-pseudo"><span class=secno>6.6.5.2.
</span>:nth-child() pseudo-class</a>
<li><a href="#nth-last-child-pseudo"><span class=secno>6.6.5.3.
</span>:nth-last-child() pseudo-class</a>
<li><a href="#nth-of-type-pseudo"><span class=secno>6.6.5.4.
</span>:nth-of-type() pseudo-class</a>
<li><a href="#nth-last-of-type-pseudo"><span class=secno>6.6.5.5.
</span>:nth-last-of-type() pseudo-class</a>
<li><a href="#first-child-pseudo"><span class=secno>6.6.5.6.
</span>:first-child pseudo-class</a>
<li><a href="#last-child-pseudo"><span class=secno>6.6.5.7.
</span>:last-child pseudo-class</a>
<li><a href="#first-of-type-pseudo"><span class=secno>6.6.5.8.
</span>:first-of-type pseudo-class</a>
<li><a href="#last-of-type-pseudo"><span class=secno>6.6.5.9.
</span>:last-of-type pseudo-class</a>
<li><a href="#only-child-pseudo"><span class=secno>6.6.5.10.
</span>:only-child pseudo-class</a>
<li><a href="#only-of-type-pseudo"><span class=secno>6.6.5.11.
</span>:only-of-type pseudo-class</a>
<li><a href="#empty-pseudo"><span class=secno>6.6.5.12.
</span>:empty pseudo-class</a>
</ul>
<li><a href="#content-selectors"><span class=secno>6.6.6.
</span>Blank</a>
<li><a href="#negation"><span class=secno>6.6.7. </span>The negation
pseudo-class</a>
</ul>
</ul>
<li><a href="#pseudo-elements"><span class=secno>7.
</span>Pseudo-elements</a>
<ul class=toc>
<li><a href="#first-line"><span class=secno>7.1. </span>The ::first-line
pseudo-element</a>
<ul class=toc>
<li><a href="#first-formatted-line"><span class=secno>7.1.1.
</span>First formatted line definition in CSS</a>
</ul>
<li><a href="#first-letter"><span class=secno>7.2. </span>The
::first-letter pseudo-element</a>
<ul class=toc>
<li><a href="#application-in-css"><span class=secno>7.2.1.
</span>Application in CSS</a>
</ul>
<li><a href="#selection"><span class=secno>7.3. </span>Blank</a>
<li><a href="#gen-content"><span class=secno>7.4. </span>The ::before
and ::after pseudo-elements</a>
</ul>
<li><a href="#combinators"><span class=secno>8. </span>Combinators</a>
<ul class=toc>
<li><a href="#descendant-combinators"><span class=secno>8.1.
</span>Descendant combinator</a>
<li><a href="#child-combinators"><span class=secno>8.2. </span>Child
combinators</a>
<li><a href="#sibling-combinators"><span class=secno>8.3. </span>Sibling
combinators</a>
<ul class=toc>
<li><a href="#adjacent-sibling-combinators"><span class=secno>8.3.1.
</span>Adjacent sibling combinator</a>
<li><a href="#general-sibling-combinators"><span class=secno>8.3.2.
</span>General sibling combinator</a>
</ul>
</ul>
<li><a href="#specificity"><span class=secno>9. </span>Calculating a
selector's specificity</a>
<li><a href="#w3cselgrammar"><span class=secno>10. </span>The grammar of
Selectors</a>
<ul class=toc>
<li><a href="#grammar"><span class=secno>10.1. </span>Grammar</a>
<li><a href="#lex"><span class=secno>10.2. </span>Lexical scanner</a>
</ul>
<li><a href="#profiling"><span class=secno>11. </span>Profiles</a>
<li><a href="#Conformance"><span class=secno>12. </span>Conformance and
requirements</a>
<li><a href="#Tests"><span class=secno>13. </span>Tests</a>
<li><a href="#ACKS"><span class=secno>14. </span>Acknowledgements</a>
<li><a href="#references"><span class=secno>15. </span>References</a>
<ul class=toc>
<li><a href="#normative-references"><span class=secno>15.1.
</span>Normative References</a>
<li><a href="#informative-references"><span class=secno>15.2.
</span>Informative References</a>
</ul>
</ul>
<!--end-toc-->
<h2 id=context><span class=secno>1. </span>Introduction</h2>
<p>Selectors Level 1 and Selectors Level 2 are defined as the subsets of
selector functionality defined in the <a
href="http://www.w3.org/TR/REC-CSS1">CSS1</a> and <a
href="http://www.w3.org/TR/CSS21/">CSS2.1</a> specifications,
respectively.
<h3 id=dependencies><span class=secno>1.1. </span>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="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
<h3 id=terminology><span class=secno>1.2. </span>Terminology</h3>
<p>All of the text of this specification is normative except examples,
notes, and sections explicitly marked as non-normative.
<p>Additional terminology is defined in the <a
href="http://www.w3.org/TR/CSS21/conform.html#defs">Definitions</a>
section of <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
Examples of document source code and fragments are given in XML <a
href="#XML10" rel=biblioentry>[XML10]<!--{{XML10}}--></a> or HTML <a
href="#HTML401" rel=biblioentry>[HTML401]<!--{{HTML401}}--></a> syntax.
<h3 id=changesFromCSS2><span class=secno>1.3. </span>Changes from CSS2</h3>
<p><em>This section is non-normative.</em>
<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>an optional namespace component is now allowed in element type
selectors, the universal selector and attribute selectors
<li>a <a href="#general-sibling-combinators">new combinator</a> has been
introduced
<li>new simple selectors including substring matching attribute selectors,
and new pseudo-classes
<li>new pseudo-elements, and introduction of the "::" convention for
pseudo-elements
<li>the grammar has been rewritten
<li>profiles to be added to specifications integrating Selectors and
defining the set of selectors which is actually supported by each
specification
<li>Selectors are now a CSS3 Module and an independent specification;
other specifications can now refer to this document independently of CSS
<li>the specification now has its own test suite
</ul>
<h2 id=selectors><span class=secno>2. </span>Selectors</h2>
<p><em>This section is non-normative, as it merely summarizes the following
sections.</em>
<p>A Selector represents a structure. This structure can be used as a
condition (e.g. in a CSS rule) that determines which elements a selector
matches in the document tree, or as a flat description of the HTML or XML
fragment corresponding to that structure.
<p>Selectors may range from simple element names to rich contextual
representations.
<p>The following table summarizes the Selector syntax:
<table class=selectorsReview>
<thead>
<tr>
<th class=pattern>Pattern
<th class=meaning>Meaning
<th class=described>Described in section
<th class=origin>First defined in CSS level
<tbody>
<tr>
<td class=pattern>*
<td class=meaning>any element
<td class=described><a href="#universal-selector">Universal selector</a>
<td class=origin>2
<tr>
<td class=pattern>E
<td class=meaning>an element of type E
<td class=described><a href="#type-selectors">Type selector</a>
<td class=origin>1
<tr>
<td class=pattern>E[foo]
<td class=meaning>an E element with a "foo" attribute
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>2
<tr>
<td class=pattern>E[foo="bar"]
<td class=meaning>an E element whose "foo" attribute value is exactly
equal to "bar"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>2
<tr>
<td class=pattern>E[foo~="bar"]
<td class=meaning>an E element whose "foo" attribute value is a list of
whitespace-separated values, one of which is exactly equal to "bar"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>2
<tr>
<td class=pattern>E[foo^="bar"]
<td class=meaning>an E element whose "foo" attribute value begins
exactly with the string "bar"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>3
<tr>
<td class=pattern>E[foo$="bar"]
<td class=meaning>an E element whose "foo" attribute value ends exactly
with the string "bar"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>3
<tr>
<td class=pattern>E[foo*="bar"]
<td class=meaning>an E element whose "foo" attribute value contains the
substring "bar"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>3
<tr>
<td class=pattern>E[foo|="en"]
<td class=meaning>an E element whose "foo" attribute has a
hyphen-separated list of values beginning (from the left) with "en"
<td class=described><a href="#attribute-selectors">Attribute
selectors</a>
<td class=origin>2
<tr>
<td class=pattern>E:root
<td class=meaning>an E element, root of the document
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:nth-child(n)
<td class=meaning>an E element, the n-th child of its parent
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:nth-last-child(n)
<td class=meaning>an E element, the n-th child of its parent, counting
from the last one
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:nth-of-type(n)
<td class=meaning>an E element, the n-th sibling of its type
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:nth-last-of-type(n)
<td class=meaning>an E element, the n-th sibling of its type, counting
from the last one
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:first-child
<td class=meaning>an E element, first child of its parent
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>2
<tr>
<td class=pattern>E:last-child
<td class=meaning>an E element, last child of its parent
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:first-of-type
<td class=meaning>an E element, first sibling of its type
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:last-of-type
<td class=meaning>an E element, last sibling of its type
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:only-child
<td class=meaning>an E element, only child of its parent
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:only-of-type
<td class=meaning>an E element, only sibling of its type
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:empty
<td class=meaning>an E element that has no children (including text
nodes)
<td class=described><a href="#structural-pseudos">Structural
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:link<br>
E:visited
<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 class=described><a href="#link">The link pseudo-classes</a>
<td class=origin>1
<tr>
<td class=pattern>E:active<br>
E:hover<br>
E:focus
<td class=meaning>an E element during certain user actions
<td class=described><a href="#useraction-pseudos">The user action
pseudo-classes</a>
<td class=origin>1 and 2
<tr>
<td class=pattern>E:target
<td class=meaning>an E element being the target of the referring URI
<td class=described><a href="#target-pseudo">The target pseudo-class</a>
<td class=origin>3
<tr>
<td class=pattern>E:lang(fr)
<td class=meaning>an element of type E in language "fr" (the document
language specifies how language is determined)
<td class=described><a href="#lang-pseudo">The :lang() pseudo-class</a>
<td class=origin>2
<tr>
<td class=pattern>E:enabled<br>
E:disabled
<td class=meaning>a user interface element E which is enabled or
disabled
<td class=described><a href="#UIstates">The UI element states
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E:checked<!--<br>E:indeterminate-->
<td class=meaning>a user interface element E which is
checked<!-- or in an
indeterminate state--> (for instance a
radio-button or checkbox)
<td class=described><a href="#UIstates">The UI element states
pseudo-classes</a>
<td class=origin>3
<tr>
<td class=pattern>E::first-line
<td class=meaning>the first formatted line of an E element
<td class=described><a href="#first-line">The ::first-line
pseudo-element</a>
<td class=origin>1
<tr>
<td class=pattern>E::first-letter
<td class=meaning>the first formatted letter of an E element
<td class=described><a href="#first-letter">The ::first-letter
pseudo-element</a>
<td class=origin>1
<tr>
<td class=pattern>E::before
<td class=meaning>generated content before an E element
<td class=described><a href="#gen-content">The ::before
pseudo-element</a>
<td class=origin>2
<tr>
<td class=pattern>E::after
<td class=meaning>generated content after an E element
<td class=described><a href="#gen-content">The ::after
pseudo-element</a>
<td class=origin>2
<tr>
<td class=pattern>E.warning
<td class=meaning>an E element whose class is "warning" (the document
language specifies how class is determined).
<td class=described><a href="#class-html">Class selectors</a>
<td class=origin>1
<tr>
<td class=pattern>E#myid
<td class=meaning>an E element with ID equal to "myid".
<td class=described><a href="#id-selectors">ID selectors</a>
<td class=origin>1
<tr>
<td class=pattern>E:not(s)
<td class=meaning>an E element that does not match simple selector s
<td class=described><a href="#negation">Negation pseudo-class</a>
<td class=origin>3
<tr>
<td class=pattern>E F
<td class=meaning>an F element descendant of an E element
<td class=described><a href="#descendant-combinators">Descendant
combinator</a>
<td class=origin>1
<tr>
<td class=pattern>E > F
<td class=meaning>an F element child of an E element
<td class=described><a href="#child-combinators">Child combinator</a>
<td class=origin>2
<tr>
<td class=pattern>E + F
<td class=meaning>an F element immediately preceded by an E element
<td class=described><a href="#adjacent-sibling-combinators">Adjacent
sibling combinator</a>
<td class=origin>2
<tr>
<td class=pattern>E ~ F
<td class=meaning>an F element preceded by an E element
<td class=described><a href="#general-sibling-combinators">General
sibling combinator</a>
<td class=origin>3
</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.
<h2 id=casesens><span class=secno>3. </span>Case sensitivity</h2>
<p>All Selectors syntax is case-insensitive within the ASCII range (i.e.
[a-z] and [A-Z] are equivalent), except for parts that are not under the
control of Selectors. The case sensitivity of document language element
names, attribute names, and attribute values in selectors depends on the
document language. For example, in HTML, element names are
case-insensitive, but in XML, they are case-sensitive. Case sensitivity of
namespace prefixes is defined in <a href="#CSS3NAMESPACE"
rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>.
<h2 id=selector-syntax><span class=secno>4. </span>Selector syntax</h2>
<p>A <dfn id=selector>selector</dfn> is a chain of one or more <a
href="#sequence">sequences of simple selectors</a> separated by <a
href="#combinators">combinators</a>. One <a
href="#pseudo-elements">pseudo-element</a> may be appended to the last
sequence of simple selectors in a selector.
<p>A <dfn id=sequence-of-simple-selectors><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>A <dfn id=simple-selector><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>, or <a href="#pseudo-classes">pseudo-class</a>.
<p><dfn id=combinators0>Combinators</dfn> are: whitespace,
"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 whitespace. Other
space-like characters, such as "em-space" (U+2003) and "ideographic space"
(U+3000), are never part of whitespace.
<p>The elements of a document tree that are represented by a selector are
the <dfn id=subjects-of-the-selector><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>An empty selector, containing no sequence of simple selectors and no
pseudo-element, is an <a href="#Conformance">invalid selector</a>.
<p>Characters in Selectors can be escaped with a backslash according to the
same <a href="http://www.w3.org/TR/CSS21/syndata.html#characters">escaping
rules</a> as CSS. <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<p id=nsdecl>Certain selectors support namespace prefixes. The mechanism by
which namespace prefixes are <dfn id=declared>declared</dfn> should be
specified by the language that uses Selectors. If the language does not
specify a namespace prefix declaration mechanism, then no prefixes are
declared. In CSS, namespace prefixes are declared with the <a
href="http://www.w3.org/TR/css3-namespace/#declaration"><code>@namespace</code></a>
rule. <a href="#CSS3NAMESPACE"
rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>
<h2 id=grouping><span class=secno>5. </span>Groups of selectors</h2>
<p>A comma-separated list of selectors represents the union of all elements
selected by each of the individual selectors in the list. (A comma is
U+002C.) For example, in CSS when several selectors share the same
declarations, they may be grouped into a comma-separated list. White space
may appear before and/or after the comma.
<div class=example>
<p>CSS example:</p>
<p>In this example, we condense three rules with identical declarations
into one. Thus,</p>
<pre>h1 { font-family: sans-serif }
h2 { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is equivalent to:</p>
<pre>h1, h2, h3 { font-family: sans-serif }</pre>
</div>
<p><strong>Warning</strong>: the equivalence is true in this example
because all the selectors are valid selectors. If just one of these
selectors were invalid, the entire group of selectors would be invalid.
This would invalidate the rule for all three heading elements, whereas in
the former case only one of the three individual heading rules would be
invalidated.
<div class=example>
<p>Invalid CSS example:</p>
<pre>h1 { font-family: sans-serif }
h2..foo { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is not equivalent to:</p>
<pre>h1, h2..foo, h3 { font-family: sans-serif }</pre>
<p>because the above selector (<code>h1, h2..foo, h3</code>) is entirely
invalid and the entire style rule is dropped. (When the selectors are not
grouped, only the rule for <code>h2..foo</code> is dropped.)</p>
</div>
<h2 id=simple-selectors><span class=secno>6. </span>Simple selectors</h2>
<h3 id=type-selectors><span class=secno>6.1. </span>Type selector</h3>
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