W3C

CSS Style Attributes

Editor's Draft 11 November 2013

This version:
http://dev.w3.org/csswg/css-style-attr/
Latest version:
http://www.w3.org/TR/css-style-attr/
Editor's draft:
http://dev.w3.org/csswg/css-style-attr/ (change log)
Previous version:
http://www.w3.org/TR/2013/PR-css-style-attr-20131003/
Feedback:
www-style@w3.org with subject line “[css-style-attr] … message topic …” (archives)
Editors:
(Mozilla, and formerly at Microsoft Corporation) <>
(Mozilla)
Previous Editors:
Bert Bos (W3C), <>
Marc Attinasi (AOL/Netscape), <>
Test suite:
http://test.csswg.org/suites/css-style-attr/nightly-unstable/

Abstract

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.

Status of this document

This is a public copy of the editors' draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don't cite this document other than as work in progress.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css-style-attr” in the subject, preferably like this: “[css-style-attr] …summary of comment…

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

For this specification to exit the CR stage, the following conditions shall be met:

  1. There must be at least two interoperable implementations. For the purposes of this criterion, we define the following terms:

    interoperable

    passing the respective test case(s) in the CSS test suite, or, if the implementation is not a Web browser, an equivalent test. Every relevant test in the test suite should have an equivalent test created if such a user agent (UA) is to be used to claim interoperability. In addition if such a UA is to be used to claim interoperability, then there must one or more additional UAs which can also pass those equivalent tests in the same way for the purpose of interoperability. The equivalent tests must be made publicly available for the purposes of peer review.

    implementation

    a user agent which:

    1. implements the specification.
    2. is available (i.e. publicly downloadable or available through some other public point of sale mechanism). This is the "show me" requirement.
    3. is shipped, or is a "nightly build" (i.e., a development version for the next release), but is not experimental (i.e., a version specifically designed to pass the test suite and not intended for daily usage going forward).
  2. A minimum of three months of the CR period must elapse. That is, this specification will not exit CR before (DATE OF PUBLICATION PLUS THREE MONTHS). When the specification exits CR, an implementation report will be published. At this point, no such report exists.

A CSS Style Attributes Test Suite will be developed during the Candidate Recommendation phase of this CSS Style Attributes specification.

Table of contents

1. Introduction

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 ‘style’ or 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 style attribute in HTML [HTML401]:

<p style="color: #090; line-height: 1.2">...</p>

2. Conformance

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:

document
A document represented in a document language that defines a style attribute for one or more of its elements.
interpreter
Someone or something that interprets the semantics of a document and its associated style information. (Most CSS user agents fall under this category.)

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.

3. Syntax and Parsing

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:

style-attribute
  : S* declaration-list
  ;

declaration-list
    : declaration [ ';' S* declaration-list ]?
    | at-rule declaration-list
    | /* empty */
    ;

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 [CSS21]), with the following addition: when the UA expects the start of a declaration or at-rule (i.e., an IDENT token or an ATKEYWORD token) but finds an unexpected token instead, that token is considered to be the first token of a malformed declaration. I.e., the rule for malformed declarations, rather than malformed statements, is used to determine which tokens to ignore in that case.

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.

Although the grammar allows it, no at-rule valid in style attributes is define at the moment. The forward-compatible parsing rules are such that a declaration following an at-rule is not ignored:

<span style="@unsupported { splines: reticulating } color: green">

4. Cascading and Interpretation

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.

5. Changes

Changes since the 2013-10-03 Proposed Recommendation are:

6. Acknowledgments

Thanks to feedback from Daniel Glazman, Ian Hickson, Eric A. Meyer, Björn Höhrmann.

7. References

Normative references

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt

Informative references

[HTML401]
Dave Raggett; Arnaud Le Hors; Ian Jacobs. HTML 4.01 Specification. 24 December 1999. W3C Recommendation. URL: http://www.w3.org/TR/1999/REC-html401-19991224
[SVG11]
Erik Dahlström; et al. Scalable Vector Graphics (SVG) 1.1 (Second Edition). 16 August 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-SVG11-20110816/