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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 4</title>
<link href="default.css" type="text/css" rel="stylesheet">
<link href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" type="text/css" rel="stylesheet">
</head>
<body>
<div class="head">
<!--logo-->
<h1 id=title>Selectors Level 4</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:
<dd>
<!-- <a href="[VERSION]">
http://www.w3.org/TR/[YEAR]/PR-[SHORTNAME]-[CDATE]</a> -->
<a href="http://dev.w3.org/csswg/selectors4">
http://dev.w3.org/csswg/selectors4</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/selectors">
http://www.w3.org/TR/selectors</a>
<dt>Previous version:
<dd><a href="http://www.w3.org/TR/css3-selectors/">
http://www.w3.org/TR/css3-selectors/</a>
<dt><a name=editors-list></a>Editors:
<dd class="vcard"><a lang="tr" class="url fn" href="http://www.tantek.com/">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>
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>
Abstract</h2>
<p><em>Selectors</em> are patterns that match against elements in a
tree, and as such form one of several technologies that can be used
to select nodes in an XML document. Selectors have been optimized for
use with HTML and XML, and are designed to be usable in
performance-critical code. They are a core component of
<acronym title="Cascading Style Sheets">CSS</acronym> (Cascading
Style Sheets), which uses Selectors to bind style properties to
elements in the document.</p>
<p>Selectors Level 4 describes the selectors that already exist in
[[!CSS3SELECT]], and further introduces new selectors for CSS and
other languages that may need them.</p>
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--status-->
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<h2 id=context>
Introduction</h2>
<h3 id="context">Background</h3>
<p><em>This section is not normative.</em>
<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. [[STTS3]]</p>
<p>Selectors Levels 1, 2, and 3 are defined as the subsets of selector
functionality defined in the <a href="http://www.w3.org/TR/REC-CSS1">CSS1</a>,
<a href="http://www.w3.org/TR/CSS21/">CSS2.1</a>, and
<a href="http://www.w3.org/TR/css3-selectors/">Selectors Level 3</a>
specifications, respectively.</p>
<h3 id="placement">Module Interactions</h3>
<p>This module replaces the definitions for, and extends the set of
selectors (aside from pseudo-element selectors) defined for CSS
in [[CSS3SELECT]] and [[CSS21]].
<p>Pseudo-element selectors, which define abstract elements in a
rendering tree, are not part of this specification: their generic syntax
is described here, but they are defined in a separate Pseudo-Element
Selectors Level 4 module.
<h3 id="conventions">Document Conventions</h3>
<p>Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words “MUST”,
“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
<p>Examples in this specification are introduced with the words “for example”
or are set apart from the normative text with <code>class="example"</code>,
like this:
<div class="example">
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word “Note” and are set apart from the
normative text with <code>class="note"</code>, like this:
<p class="note">Note, this is an informative note.</p>
<h2 id=overview>
Selectors Overview</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 data">
<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
whitespace-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[foo|="en"]</td>
<td class="meaning">an E element whose "foo" 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&g
133E
t;
<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.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 id=syntax>
Selector Syntax</h2>
<h3 id=structure>
Structure and Terminology</h2>
<p>A <dfn>selector</dfn> is a chain of one
or more <a href="#compound">compound selectors</a>
separated by <a href="#combinators">combinators</a>.</p>
<p>A <dfn><a name=compound>compound selector</a></dfn>
is a chain of <a href="#simple">simple selectors</a>
that are not separated by a <a href="#combinators">combinator</a>. It
always begins with a <a href="#type-selectors">type selector</a> or a
(possibly implied) <a href="#universal-selector">universal selector</a>.
No other type selector or universal selector is allowed in the sequence.</p>
<p>A <dfn><a name=simple></a><a
href="#simple">simple selector</a></dfn> is either a <a
href="#type-selectors">type selector</a>, <a
href="#universal-selector">universal selector</a>, <a
href="#attribute-selectors">attribute selector</a>, <a
href="#class-html">class selector</a>, <a
href="#id-selectors">ID selector</a>, or <a
href="#pseudo-classes">pseudo-class</a>.</p>
<p><dfn id=combinator>Combinators</dfn> are punctuation that represent a particular
kind of relationship between the compound selectors on either side.
Combinators in Selectors level 4 include: whitespace, "greater-than
sign" (U+003E, <code>></code>), "plus sign" (U+002B,
<code>+</code>) and "tilde" (U+007E, <code>~</code>).
<a href="#whitespace">White space</a> may appear between a combinator
and the simple selectors around it.</p>
<p>An empty selector, containing no compound selector, is an
<a href="#invalid">invalid selector</a>.</p>
<h3 id=subject>
Subject of a Selector
<p>The elements of a document tree that are represented by a selector
are the <dfn>subjects</dfn> of the selector.
<p>By default, the subjects of a selector are the elements represented
by the last compound selector in the selector. Thus a selector consisting
of a single compound selector represents any element satisfying its
requirements. Prepending another compound selector and a combinator
to a sequence imposes additional matching constraints, so the subjects of
the selector are always a subset of the elements represented by the last
compound selector.</p>
<p>The subject of the selector can be explicitly identified by prepending
an exclamation mark (!) to one of the compound selectors in a selector.
Although the element structure that the selector represents is the same
with or without the exclamation mark, indicating the subject in this way
can change which compound selector represents the subject in that structure.
<div class="example">
<p>For example, the following selector represents a list item <code>LI</code>
unique child of an ordered list <code>OL</code>:
<pre>OL > LI:only-child</pre>
<p>However the following one represents an ordered list <code>OL</code>
having a unique child, that child being a <code>LI</code>:
<pre>!OL > LI:only-child</pre>
<p>The structures represented by these two selectors are the same, but the
subjects of the selectors are not.
</div>
<h3 id=case-sensitive>
Characters and case sensitivity</h3>
<p>All Selectors syntax is case-insensitive within the ASCII range
(i.e. [a-z] and [A-Z] are equivalent), except for parts that are
not under the control of Selectors. The case sensitivity of document
language element names, attribute names, and attribute values in
selectors depends on the document language. For example, in HTML,
element names are case-insensitive, but in XML, they are
case-sensitive. Case sensitivity of namespace prefixes is defined in
[[!CSS3NAMESPACE]].</p>
<p><dfn id=whitespace>White space</dfn> in Selectors consists of the
characters SPACE (U+0020), TAB (U+0009), LINE FEED (U+000A),
CARRIAGE RETURN (U+000D), and FORM FEED (U+000C) can occur in whitespace.
Other space-like characters, such as EM SPACE (U+2003) and
IDEOGRAPHIC SPACE (U+3000), are never part of white space.
<p>Characters in Selectors can be escaped with a backslash according
to the same <a href="http://www.w3.org/TR/CSS21/syndata.html#characters">escaping
rules</a> as CSS. [[!CSS21]].</p>
<h3 id="namespaces">
Namespaces</h3>
<p>Certain selectors support namespace prefixes. The
mechanism by which namespace prefixes are <dfn>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. [[!CSS3NAMESPACE]]</p>
<h3 id=invalid>
Invalid Selectors and Error Handling</h3>
<p>Invalidity is caused by a parsing error, e.g. an unrecognized token or a token
which is not allowed at the current parsing point.
<p>User agents must observe the rules for handling parsing errors:
<ul>
<li>a simple selector containing an <a href="#namespaces">undeclared namespace prefix</a> is invalid</li>
<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 class="issue">It's been <a href="http://lists.w3.org/Archives/Public/www-style/2010Nov/0203.html">requested</a>
that the last rule be dropped in favor of Media Queries-style error-handling.</p>
<h2 id=logical-combination>
Logical Combinations</h2>
<h3 id=grouping>
Selector Groups</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.</p>
<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.</p>
<div class="example">
<p>Invalid CSS example:</p>
<pre>h1 { font-family: sans-serif }
h2..foo { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is not equivalent to:</p>
<pre>h1, h2..foo, h3 { font-family: sans-serif }</pre>
<p>because the above selector (<code>h1, h2..foo, h3</code>)
is entirely invalid and the entire style rule is dropped. (When
the selectors are not grouped, only the rule for <code>h2..foo</code>
is dropped.)</p>
</div>
<h3 id=matches>
The Matches-Any Pseudo-class: '':matches()''</h3>
<p>The matches pseudo-class, <code>:matches(<var>X</var>)</code>,
is a functional notation taking a <a href="#grouping">selector group</a>
as an argument. It represents an element that is represented by its argument.
<p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
are allowed within <code>:matches()</code>:
<a href="#combinator">combinators</a> are not allowed. Additionally,
<code>:matches()</code> may not be nested within itself or within
<code>:not()</code>: <code>:matches(:matches(...))</code> and
<code>:not(:matches(...))</code> are invalid.</p>
<p>Pseudo-elements cannot be represented by the matches pseudo-class;
they are not valid within <code>:matches()</code>.
<p>Default namespace declarations do not affect the subject of any selector
within a matches-any pseudo-class unless the argument is an explicit
universal selector or a type selector.</p>
<div class="example">
<p>For example, following selector matches any element that is being
hovered or focused, regardless of its namespace. In particular, it
is not limited to only matching elements in the default namespace
that are being hovered or focused.</p>
<pre>*|*:matches(:hover, :focus)</pre>
<p>The following selector, however, represents only hovered or focused
elements that are in the default namespace, because it uses an explicit
universal selector within the <code>:matches()</code> notation:</p>
<pre>*|*:matches(*:hover, *:focus)</pre>
</div>
<h3 id=negation>
The Negation Pseudo-class: '':not()''</h3>
<p>The negation pseudo-class, <code>:not(<var>X</var>)</code>, is a
functional notation taking a <a href="#grouping">selector group</a>
as an argument. It represents an element that is not represented
by its argument.
<p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
are allowed within <code>:matches()</code>:
<a href="#combinator">combinators</a> are not allowed. Additionally,
negations may not be nested within itself or within <code>:matches()</code>:
<code>:not(:not(...))</code> and <code>:matches(:not(...))</code> are invalid.
<p>Pseudo-elements cannot be represented by the negation pseudo-class;
they are not valid within <code>:not()</code>.
<div class="example">
<p>For example, the following selector matches all <code>button</code>
elements in an HTML document that are not disabled.</p>
<pre>button:not([DISABLED])</pre>
<p>The following selector represents all but <code>FOO</code>
elements.</p>
<pre>*:not(FOO)</pre>
<p>The following compound selector represents all HTML elements
except links.</p>
<pre>html|*:not(:link):not(:visited)</pre>
</div>
<p>Default namespace declarations do not affect the subject of any selector
within a negation pseudo-class unless the argument is an explicit universal
selector or a type selector. (See <a href="#matches"><code>:matches()</code></a>
for examples.</p>
<p class="note"><strong>Note</strong>: the :not() pseudo allows
useless selectors to be written. For instance <code>:not(*|*)</code>,
which represents no element at all, or <code>foo:not(bar)</code>,
which is equivalent to <code>foo</code> but with a higher
specificity.</p>
<h2 id=elemental-selectors>
Elemental selectors</h2>
<h3 id=type-selectors>
Type selector</h3>
<p>A <dfn>type selector</dfn> is the name of a document language
element type written using the syntax of
<a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
names</a> [[!CSS3NAMESPACE]]. 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 id=typenmsp>
Type selectors and namespaces</h4>
<p>Type selectors allow an optional namespace component: a namespace
prefix that has been previously <a href="#nsdecl">declared</a> may be
prepended to the element name separated by the namespace separator
"vertical bar" (U+007C, <code>|</code>). (See, e.g., [[XML-NAMES]] for the use of namespaces in
XML.)</p>
<p>The namespace component may be left empty (no prefix before the
namespace separator) to indicate that the selector is only to
represent elements with no namespace.</p>
<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 <a href="#nsdecl">declared</a> for namespaced selectors (e.g. in CSS, in
the style sheet). If a default namespace has been declared, such
selectors will represent only elements in the default namespace.</p>
<p>A type selector containing a namespace prefix that has not been
previously <a href="#nsdecl">declared</a> for namespaced selectors is
an <a href="#Conformance">invalid</a> selector.</p>
<p>In a namespace-aware client, the name part of element type
selectors (the part after the namespace separator, if it is present)
will only match against the <a
href="http://www.w3.org/TR/REC-xml-names/#NT-LocalPart">local part</a>
of the element's <a
href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">qualified
name</a>.</p>
<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 a
namespace</dd>
<dt><code>|E</code></dt>
<dd>elements with name E without a namespace</dd>
<dt><code>E</code></dt>
<dd>if no default namespace has been <a href="#nsdecl">declared</a> for selectors, this is
equivalent to *|E. Otherwise it is equivalent to ns|E where ns is
the default namespace.</dd>
</dl>
<div class="example">
<p>CSS examples:</p>
<pre>@namespace foo url(http://www.example.com);
foo|h1 { color: blue } /* first rule */
foo|* { color: yellow } /* second rule */
|h1 { color: red } /* ...*/
*|h1 { color: green }
h1 { color: green }</pre>
<p>The first rule (not counting the <code>@namespace</code> at-rule)
will match only <code>h1</code> elements in the
"http://www.example.com" namespace.</p>
<p>The second rule will match all elements in the
"http://www.example.com" namespace.</p>
<p>The third rule will match only <code>h1</code> elements with
no namespace.</p>
<p>The fourth rule will match <code>h1</code> elements in any
namespace (including those without any namespace).</p>
<p>The last rule is equivalent to the fourth rule because no default
namespace has been defined.</p>
</div>
<h3 id=universal-selector>
Universal selector </h3>
<p>The <dfn>universal selector</dfn>, written as a
<a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
name</a> [[!CSS3NAMESPACE]] with an asterisk (<code>*</code>
U+002A) as the local name, represents the qualified name of any element
type. It represents any single element in the document tree in any
namespace (including those without a namespace) if no default
namespace has been specified for selectors. If a default namespace has
been specified, see <a href="#univnmsp">Universal selector and
Namespaces</a> below.</p>
<p>If a universal selector represented by <code>*</code> (i.e. without a
namespace prefix) is not the only component of a <a href="#compound">compound
selector</a> or is immediately followed by a
<a href="#pseudo-elements">pseudo-element</a>, then the <code>*</code> may
be omitted and the universal selector's presence implied.</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> not be omitted, because it decreases the potential
confusion between, for example,
<code style="white-space: nowrap">div :first-child</code>
and <code style="white-space: nowrap">div:first-child</code>.
Here, <code style="white-space: nowrap">div *:first-child</code>
is more readable.</p>
<h4 id=univnmsp>
Universal selector and namespaces</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 a 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 <a href="#nsdecl">declared</a> is an <a
href="#Conformance">invalid</a> selector.</p>
<h2 id=attribute-selectors>
Attribute selectors</h2>
<p>Selectors allow the representation of an element's attributes. When
a selector is used as an expression to match against an element,
attribute selectors must be considered to match an element if that
element has an attribute that matches the attribute represented by the
attribute selector.</p>
<h3 id=attribute-representation>
Attribute presence and value selectors</h3>
<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). Also if "val" is the empty string, it will never represent
anything.</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>a</code> element in HTML) as described in BCP 47 ([[BCP47]]) or its successor. For
<code>lang</code> (or <code>xml:lang</code>) language subcode
matching, please see <a href="#lang-pseudo">the <code>:lang</code>
pseudo-class</a>.</dd>
</dl>
<p>Attribute values must be CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>. [[!CSS21]]
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 CSS rules illustrate the differences between
"=" and "~=". The first selector would match, for example, an
<code>a</code> element with the value "copyright copyleft
copyeditor" on a <code>rel</code> attribute. The second selector
would only match an <code>a</code> element with an <code>href</code>
attribute having the exact value "http://www.w3.org/".</p>
<pre>a[rel~="copyright"] { ... }
a[href="http://www.w3.org/"] { ... }</pre>
<p>The following selector represents an <code>a</code> element
whose <code>hreflang</code> attribute is exactly "fr".</p>
<pre>a[hreflang=fr]</pre>
<p>The following selector represents an <code>a</code> element for
which the value of the <code>hreflang</code> attribute begins with
"en", including "en", "en-US", and "en-scouse":</p>
<pre>a[hreflang|="en"]</pre>
<p>The following selectors represent a <code>DIALOGUE</code> element
whenever it has one of two different values for an attribute
<code>character</code>:</p>
<pre>DIALOGUE[character=romeo]
DIALOGUE[character=juliet]</pre>
</div>
<h3 id=attribute-substrings>
Substring matching attribute selectors</h3>
<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". If "val" is the empty string then the selector does not
represent anything.</dd>
<dt><code>[att$=val]</code>
<dd>Represents an element with the <code>att</code> attribute whose value ends with
the suffix "val". If "val" is the empty string then the selector does not represent
anything.</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". If "val" is the empty string then
the selector does not represent anything.</dd>
</dl>
<p>Attribute values must be CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>. [[!CSS21]]
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>
<h3 id=attrnmsp>
Attribute selectors and namespaces</h3>
<p>The attribute name in an attribute selector is given as a
<a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
name</a>: a namespace prefix that has been previously <a href="#nsdecl">declared</a>
may be prepended to the attribute name separated by the namespace
separator "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 namespace (equivalent
to "<code>|attr</code>"; these attributes are said to be in the
"per-element-type namespace partition"). An asterisk may be used for
the namespace prefix indicating that the selector is to match all
attribute names without regard to the attribute's namespace.
<p>An attribute selector with an attribute name containing a namespace
prefix that has not been previously <a href="#nsdecl">declared</a> is
an <a href="#Conformance">invalid</a> selector.</p>
<div class="example">
<p>CSS examples:</p>
<pre>@namespace foo "http://www.example.com";
[foo|att=val] { color: blue }
[*|att] { color: yellow }
[|att] { color: green }
[att] { color: green }</pre>
<p>The first rule will match only elements with the attribute
<code>att</code> in the "http://www.example.com" namespace with the
value "val".</p>
<p>The second rule will match only elements with the attribute
<code>att</code> regardless of the namespace of the attribute
(including no namespace).</p>
<p>The last two rules are equivalent and will match only elements
with the attribute <code>att</code> where the attribute is not
in a namespace.</p>
</div>
<h3 id=def-values>
Default attribute values in DTDs</h3>
<p>Attribute selectors represent attribute values in the document tree.
How that document tree is constructed is outside the scope of Selectors.
In some document formats default attribute values can be defined in a DTD or
elsewhere, but these can only be selected by attribute selectors if they
appear in the document tree. Selectors should be designed so that they
work whether or not the default values are included in the document tree.</p>
<p>For example, a XML UA may, but is <em>not</em> required to read an "external
subset" of the DTD but <em>is</em> required to look for default
attribute values in the document's "internal subset." (See, e.g., [[XML10]] for definitions of these subsets.) Depending