Markup languages such as HTML [HTML40] and SVG [SVG11] provide a styling attribute on most elements, to hold a fragment of a style sheet that applies to those elements. One of the possible style sheet languages is CSS. This draft describes the syntax and interpretation of the CSS fragment that can be used in such styling attributes.
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This document was produced by the CSS Working Group (part of the Style Activity).
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This specification is a Last Call Working Draft. All persons are encouraged to review this document and send comments to the www-style mailing list as described above. The deadline for comments is 9 February 2010.
A CSS Styling Attribute Test Suite will be developed during the Candidate Recommendation phase of this CSS Styling Attribute specification.
Some document formats have a styling attribute to permit the author to directly apply style information to specific elements in documents. If a document format defines a styling attribute and the attribute accepts CSS as its value, then this specification defines that CSS styling attribute’s syntax and interpretation.
The following example shows the use of the
in HTML [HTML40]:
<p style="color: #090; line-height: 1.2">...</p>
A document or implementation cannot conform to CSS Styling Attributes Level 1 alone, but can claim conformance to CSS Styling Attributes Level 1 if it satisfies the conformance requirements in this specification when implementing CSS together with styling attribute handling as defined in a document language that has CSS styling attributes.
Conformance to CSS Styling Attributes Level 1 is defined for two classes:
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. 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. [RFC2119]
Examples in this specification are introduced with the words "for
example" or are set apart from the normative text with
class="example", like this:
This is an example of an informative example.
Informative notes begin with the word "Note" and are set apart from the
normative text with
class="note", like this:
Note, this is an informative note.
The value of the styling attribute must match the syntax of the contents of a CSS declaration block, whose formal grammar is given below in terms of the CSS core grammar:
declaration-list : S* declaration? [ ';' S* declaration? ]* ;
Note that following the CSS2.1 convention, comment tokens are not shown in the rule above.
The interpreter must parse the styling attribute's value using the same forward-compatible parsing rules that apply to parsing declaration block contents in a normal CSS style sheet. See chapter 4 of the CSS2.1 specification for details. [CSS21]
Note that because there is no open brace delimiting the
declaration list in the CSS styling attribute syntax, a close brace
}) in the styling attribute's value does not terminate the
style data: it is merely an invalid token.
The declarations in a styling attribute apply to the element to which the attribute belongs. CSS2.1 defines how style sheets and styling attributes are cascaded together. [CSS21] Relative URLs in the style data must be resolved relative to the styling attribute's element (or to the document if per-element resolution is not defined) when the attribute's value is parsed.
Aside from the differences in cascading, the declarations in a styling attribute must be interpreted exactly as if they were given in a CSS style rule that applies to the element.
The CSS Working Group strongly recommends that document languages do not allow multiple CSS styling attributes on a single element. If a document language allows multiple CSS styling attributes, each must be parsed independently and treated as a separate style rule, the ordering of which should be defined by the document language, else is undefined.
Thanks to feedback from Daniel Glazman, Ian Hickson, Eric A. Meyer, Björn Höhrmann.