CSS Style Attributes

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. 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 style attributes.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document was produced by the CSS Working Group as a Candidate Recommendation.

A Candidate Recommendation is a document that has been widely reviewed and is ready for implementation. W3C encourages everybody to implement this specification and return comments to the (archived) public mailing list www-style@w3.org (see instructions). When sending e-mail, please put the text “css-style-attr” in the subject, preferably like this: “[css-style-attr] …summary of comment…”

Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

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 one month of the CR period must elapse. That is, this specification will not exit CR before 14 November 2010. 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.

Changes since the last Working Draft are listed in the Disposition of Comments.

Table of contents

• 1. Introduction
• 2. Conformance
• 3. Syntax and Parsing
• 4. Cascading and Interpretation
• 5. Acknowledgments
• 6. References
  • Normative references
  • Informative references

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.

<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:

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:

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.

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. Acknowledgments

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

6. References

Normative references

[CSS21]

Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 8 September 2009. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2009/CR-CSS2-20090908

[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]

David Raggett; Ian Jacobs; Arnaud Le Hors. 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). 22 June 2010. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2010/WD-SVG11-20100622