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This CSS module defines the syntax for using namespaces in CSS. It
introduces the @namespace
rule for declaring the default
namespace and binding namespaces to namespace prefixes, and it defines a
syntax that other specifications can adopt for using those prefixes in
namespace-qualified names.
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This document was produced by the CSS Working Group (part of the Style Activity).
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This is a draft of a module of CSS (Cascading Style Sheets). It is derived with minimal change from the CSS3 Namespace Enhancements 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].
@namespace
rule
This section is informative.
This specification defines the syntax for using namespaces in CSS. It
introduces the @namespace
rule for declaring a default
namespace and for binding namespaces to namespace prefixes. This
specification also defines a syntax for using those prefixes in
namespace-qualified names, but does not define where such names are valid
or what they mean. The terminology used in this specification is that of
[XML-NAMES11]. Do we really need this sentence?
It should be noted that a CSS client that does not support this module will (if it properly conforms to CSS forward compatible parsing rules) 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.
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.
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 examples, notes, and sections explicitly marked as non-normative.
@namespace
ruleThe @namespace at-rule declares a namespace prefix and associates it with a given namespace (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].
@namespace "http://www.w3.org/1999/xhtml"; @namespace svg "http://www.w3.org/2000/svg";
The first rule declares a default namespace
http://www.w3.org/1999/xhtml
to be applied to names that
have no explicit namespace component.
The second rule declares a namespace prefix svg
that is
used to apply the namespace http://www.w3.org/2000/svg
where the svg
namespace prefix is used.
In CSS Namespaces, as in XML Namespaces [REC-XML-NAMES], the local prefix is merely a syntactic construct; it is the expanded name (the tuple of local name and namespace) 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.
The syntax for the @namespace rule is as follows (using the notation from the Grammar appendix of CSS2.1 [CSS21]):
namespace
: NAMESPACE_SYM S* [namespace_prefix S*]? [STRING|URI] S* ';'
S*
;
namespace_prefix
: IDENT
;
with the new token:
"@namespace" {return NAMESPACE_SYM;}
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 [ namespace [S|CDO|CDC]* ]*
immediately after [ import [S|CDO|CDC]* ]*
in the
stylesheet
grammar.
A syntactically invalid @namespace
rule (whether malformed
or misplaced) must be ignored. A style
sheet containing an invalid @namespace
rule is
non-conforming.
A URI string parsed from the url()
syntax must be treated
as a literal string: no URI-specific normalization is applied. For this
reason the string syntax is recommended, and the url()
syntax discouraged deprecated?.
The namespace prefix is declared only within the style sheet in which its @namespace rule appears, and not any style sheets imported by that style sheet, style sheets that import that style sheet, or any other style sheets applying to the document.
A namespace prefix, once declared, represents the namespace for which it was declared and can be used to indicate the namespace of a namespace-qualified name.
If in the namespace declaration the namespace prefix is omitted, then the namespace so declared is the default namespace. The default namespace 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 [REC-XML-NAMES], in Selectors [SELECT] the default namespace applies to type selectors—but it does not apply to attribute selectors. There is no default 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.
Namespace prefixes are, like CSS property names, case-insensitive.
If a namespace prefix or default namespace is declared more than once only the last declaration shall be used.
A qualified name 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" (|
, 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 (*
, U+002A) as a wildcard
prefix to indicate a name in any namespace, including no namespace.
Given the namespace declarations:
@namespace toto "http://toto.example.org"; @namespace "http://example.com/foo";
In a context where the default namespace applies
toto|A
A
in the
http://toto.example.org
namespace.
|B
B
that belongs to no namespace.
*|C
C
in any namespace, including no
namespace.
D
D
in the
http://example.com/foo
namespace.
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.
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 Ian Hickson, Bjöern Höhrmann, Anne van Kesteren, and L. David Baron for their comments.