Markup languages such as HTML [HTML401] and SVG [SVG11] provide a style attribute on most elements, to hold inline style information that applies to those elements. This draft describes the syntax and interpretation of the CSS fragment that can be used in such style attributes.
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Please see the Working Group's implementation report. One test is not passed, although this is due to bugs in browser implementation of xml:base and attribute (non)ordering, not the style attribute itself. The equivalent test for HTML (including the xml serialisation of HTML5) is passed by multiple implementations.
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Some document formats have a style
attribute to permit the author to directly apply style information
to specific elements in documents. If a document format defines a style
attribute (whether named ‘
something else) and the attribute accepts CSS as its value, then this
specification defines that style
attribute’s syntax and interpretation.
The following example shows the use of the
in HTML [HTML401]:
<p style="color: #090; line-height: 1.2">...</p>
A document or implementation cannot conform to CSS Style Attributes alone, but can claim conformance to CSS Style Attributes if it satisfies the conformance requirements in this specification when implementing CSS together with style attribute handling as defined in a document language that has one or more CSS style attributes.
Conformance to CSS Style Attributes 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 style attribute must match the syntax of the contents of a CSS declaration block (excluding the delimiting braces), whose formal grammar is given below in the terms and conventions 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 style 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 style attribute syntax, a close brace
}) in the style attribute's value does not terminate the
style data: it is merely an invalid token.
The declarations in a style attribute apply to the element to which the attribute belongs. In the cascade, these declarations are considered to have author origin and a specificity higher than any selector. CSS2.1 defines how style sheets and style attributes are cascaded together. [CSS21] Relative URLs in the style data must be resolved relative to the style 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 style 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 style attributes on a single element. If a document language allows multiple CSS style 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.