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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Namespaces Module</title>
<link rel="stylesheet" type="text/css" href="../default.css">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED">
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Namespaces Module</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE: 31 October 2007]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-namespace/">http://dev.w3.org/csswg/css3-namespace/</a></dd>
<!--
<dd><a href="http://www.w3.org/TR/[YEAR]/WD-css3-namespace-[CDATE]/">http://www.w3.org/TR/[YEAR]/WD-css3-namespace-[CDATE]/</a></dd>
-->
<dt>Latest version:</dt>
<dd><a href="http://www.w3.org/TR/css3-namespace">http://www.w3.org/TR/css3-namespace</a></dd>
<dt>Previous version:</dt>
<dd><a href="http://www.w3.org/TR/2006/WD-css3-namespace-20060828/">http://www.w3.org/TR/2006/WD-css3-namespace-20060828/</a></dd>
<dt>Editor:</dt>
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a></dd>
<dd><a href="http://annevankesteren.nl/contact">Anne van Kesteren</a></dd>
<dt>Previous Editors:</dt>
<dd>Peter Linss, Netscape Communications</dd>
<dd>Chris Lilley, W3C</dd>
</dl>
<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>This CSS module defines the syntax for using namespaces in CSS.
It introduces the <code>@namespace</code> rule for declaring the
default namespace and binding namespaces to namespace prefixes, and
it also defines a syntax that other specifications can adopt for using
those prefixes in namespace-qualified names.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--begin-status-->
<!--end-status-->
<p>This is a draft of a module of CSS (Cascading Style Sheets). It is derived
with minimal change from the
<a href="http://www.w3.org/1999/06/25/WD-css3-namespace-19990625/">CSS3 Namespace Enhancements</a>
syntax proposal from 1999 with which the CSS WG has been in agreement
for many years and which is already implemented in user agents. The material
from that proposal found its way into drafts of [[SELECT]], [[CSS3SYN]]
and [[CSS3VAL]]. [[SELECT]] is currently a Candidate Recommendation.
Unfortunately, [[CSS3SYN]] has dependencies on (potentially) all other
CSS3 modules and this, plus work on CSS2.1, has delayed the availability
of this specification. To break the chain of dependencies and allow faster
progress on the Recommendation track, the present module has been split out.
It is primarily intended as a CSS module, though it could also be referenced
by [[SVG12]] or indeed [[!CSS21]].</p>
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<div>
<h2 id="intro">Introduction</h2>
<p><em>This section is non-normative.</em></p>
<p>The CSS Namespaces module defines syntax for using namespaces in CSS.
It introduces the <code>@namespace</code> rule for declaring a
default namespace and for binding namespaces to namespace prefixes.
It also defines a syntax for using those prefixes to represent
namespace-qualified names. It does not define where such names are
valid or what they mean: that depends on their context and is defined
by a host language (such as [[Selectors]]) that references the syntax
defined in CSS Namespaces.
<p>The terminology used in this specification is that of [[XML-NAMES11]].
<span class="issue">Do we really need this sentence?</span>
However, the syntax defined here is not restricted to representing XML
element and attribute names.</p>
<p>Note that a CSS client that does not support this module will (if it
properly conforms to
<a href="http://www.w3.org/TR/CSS21/syndata.html#parsing-errors">CSS's
forward-compatible parsing rules</a>)
ignore all @namespace rules, as well as all style rules that make use
of namespace qualified names. The syntax of delimiting namespace
prefixes in CSS was deliberately chosen so that these CSS clients would
ignore the style rules rather than possibly match them incorrectly.</p>
</div>
<div>
<h2 id="conformance">Conformance</h2>
<p>A document or implementation cannot conform to this specification alone,
but can claim conformance to this specification if it satisfies the
conformance requirements in this specification when implementing CSS or
another host language that normatively references this specification.</p>
<p>Conformance to this specification is defined for three classes:
<dl>
<dt><dfn>style sheet</dfn></dt>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#x10">CSS style
sheet</a> (or a complete unit of another host language that normatively
references CSS Namespaces).
<dt><dfn>author</dfn></dt>
<dd>Someone or something that creates a style sheet.</dd>
<dt><dfn>interpreter</dfn></dt>
<dd>Someone or something that interprets the semantics of a style sheet.
(CSS <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">user
agents</a> fall under this category.)</dd>
</dl>
<p>The 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 (see [[!RFC2119]]).
However, for readability, these words do not appear in all uppercase
letters in this specification. All of the text of this specification is
normative except sections explicitly marked as non-normative, examples,
and notes.</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>
</div>
<div>
<h2 id="declaration">Declaring namespaces: the <code>@namespace</code> rule</h2>
<p>The @namespace <a href="http://www.w3.org/TR/CSS21/syndata.html#q6">at-rule</a>
declares a namespace prefix and associates it with a given namespace name
(a string). This namespace prefix can then be used in namespace-qualified
names such as those described in the Selectors Module [[SELECT]] or the
Values and Units module [[CSS3VAL]].</p>
<div class="example">
<pre>@namespace "http://www.w3.org/1999/xhtml";
<!-- -->@namespace svg "http://www.w3.org/2000/svg";</pre>
<p>The first rule declares a default namespace
<code>http://www.w3.org/1999/xhtml</code> to be applied to names that
have no explicit namespace component.</p>
<p>The second rule declares a namespace prefix <code>svg</code> that
is used to apply the namespace <code>http://www.w3.org/2000/svg</code>
where the <code>svg</code> namespace prefix is used.</p>
</div>
<p id="expanded-name-match">In CSS Namespaces, as in XML Namespaces
[[XML-NAMES11]], the prefix is merely a syntactic construct; it is
the <em><dfn id="expanded-name">expanded name</dfn></em> (the tuple of
local name and namespace name) that is significant.
Thus the actual prefixes used in a CSS style sheet, and whether they are
defaulted or not, are independent of the namespace prefixes used in the
markup and whether these are defaulted or not.</p>
<h3 id="syntax">Syntax</h3>
<p>The syntax for the @namespace rule is as follows (using the notation from
the <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar appendix of
CSS 2.1</a> [[!CSS21]]):</p>
<pre><!--
-->namespace
<!-- --> : NAMESPACE_SYM S* [namespace_prefix S*]? [STRING|URI] S* ';' S*
<!-- --> ;
<!-- -->namespace_prefix
<!-- --> : IDENT
<!-- --> ;<!--
--></pre>
<p>with the new token:</p>
<pre>"@namespace" {return NAMESPACE_SYM;}</pre>
<p>Any @namespace rules must follow all @charset and @import rules and precede
all other non-ignored at-rules and rule sets in a style sheet.
For CSS syntax this adds <code>[ namespace [S|CDO|CDC]* ]*</code>
immediately after <code>[ import [S|CDO|CDC]* ]*</code> in the
<code>stylesheet</code> grammar.</p>
<p>A syntactically invalid <code>@namespace</code> rule (whether malformed or
misplaced) must be <a href="http://www.w3.org/TR/CSS21/conform.html#x22">ignored</a>.
A style sheet containing an invalid <code>@namespace</code> rule is
non-conforming.</p>
<p>A URI string parsed from the <code>URI</code> syntax must be treated as
a literal string: as with the <code>STRING</code> syntax, no URI-specific
normalization is applied. For this reason the string syntax is recommended,
and the <code>url()</code> syntax discouraged <span class="issue">deprecated?</span>.</p>
<h3 id="scope">Scope</h3>
<p>The namespace prefix is declared only within the style sheet in which its
@namespace rule appears. It is not declared in any style sheets importing or
imported by that style sheet, nor in any other style sheets applying to the
document.</p>
<h3 id="prefixes">Declaring Prefixes</h3>
<p>A <dfn>namespace prefix</dfn>, once declared, represents the namespace for
which it was declared and can be used to indicate the namespace of a
namespace-qualified name.</p>
<p>If in the namespace declaration the namespace prefix is omitted, then the
namespace so declared is the default namespace. The <dfn>default
namespace</dfn> applies to names that have no explicit namespace prefix.
Modules that employ namespace prefixes must define in which contexts the
default namespace applies. For example, following [[XML-NAMES11]], in
Selectors [[SELECT]] the default namespace applies to type
selectors—but it does not apply to attribute selectors. There is no
default value for the default namespace: modules that assign unqualified
names to the default namespace must define how those unqualified names are
to be interpreted when no default namespace is declared.</p>
<p>Namespace prefixes are, <a href="http://www.w3.org/TR/CSS21/syndata.html#q6">like
CSS property names</a>, case-insensitive.</p>
<p class="note">Note, this does not cause any conflict with languages that
use case-sensitive prefixes because <a href="#expanded-name-match">only the
expanded name matters</a>, not the prefix, and therefore the prefixes need
not be identical for the names to match.</p>
<p>If a namespace prefix or default namespace is declared more than once only
the last declaration shall be used.</p>
</div>
<div>
<h2 id="css-qnames">CSS Qualified Names</h2>
<p>A <dfn>qualified name</dfn> is a name explicitly located within (associated
with) a namespace. To form a qualified name in CSS syntax, a namespace
prefix that has been declared within scope is prepended to a local name
(such as an element or attribute name), separated by a "vertical bar"
(<code>|</code>, U+007C). The prefix, representing the namespace for which
it has been declared, indicates the namespace of the local name.
The prefix of a qualified name may be omitted to indicate that the name
belongs to no namespace. Some contexts may allow the use of an asterisk
(<code>*</code>, U+002A) as a wildcard prefix to indicate a name in any
namespace, including no namespace.</p>
<div class="example">
<p>Given the namespace declarations:</p>
<pre>@namespace toto "http://toto.example.org";
<!-- -->@namespace "http://example.com/foo";</pre>
<p>In a context where the default namespace applies</p>
<dl>
<dt><code>toto|A</code></dt>
<dd>represents the name <code>A</code> in the <code>http://toto.example.org</code>
namespace.</dd>
<dt><code>|B</code></dt>
<dd>represents the name <code>B</code> that belongs to no namespace.</dd>
<dt><code>*|C</code></dt>
<dd>represents the name <code>C</code> in any namespace, including no
namespace.</dd>
<dt><code>D</code></dt>
<dd>represents the name <code>D</code> in the <code>http://example.com/foo</code>
namespace.</dd>
</dl>
</div>
<p>CSS qualified names can be used in (for example) selectors and property
values as described in other modules. Those modules should define the use
of a namespace prefix that has not been properly declared as a parsing error
that will cause the selector or declaration (etc.) to be considered invalid
and ignored.</p>
</div>
<h2 class="no-num" id="acknowledgments">Acknowledgments</h2>
<p>This draft borrows heavily from earlier drafts on CSS namespace support
by Chris Lilley and by Peter Linss [[CSS3NAMESPACE]] and early (unpublished)
drafts on CSS and XML by Håkon Lie and Bert Bos, and XML Namespaces
and CSS by Bert Bos and Steven Pemberton. Many current and former members of
the CSS Working Group have contributed to this document. Discussions on
www-style@w3.org and in other places have also contributed ideas to this
specification. Special thanks goes to L. David Baron, Ian Hickson, Bjöern
Höhrmann, Lachlan Hunt, and Anne van Kesteren for their comments.</p>
<h2 class="no-num" id="references">References</h2>
<h3 class="no-num" id="normative-references">Normative references</h3>
<!--begin-normative-->
<p>[Here will be inserted the file "normative.inc"]</p>
<!--end-normative-->
<h3 class="no-num" id="informative-references">Informative references</h3>
<!--begin-informative-->
<p>[Here will be inserted the file "informative.inc"]</p>
<!--end-informative-->
</body>
</html>
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