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. This module describes the syntax and interpretation of the CSS fragment that can be used in such style attributes.

Status of this document

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>

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.

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.

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

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.

Changes

• Parse at-rules in declaration lists to allow future extension.

Acknowledgments

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

References

Normative references

[Here will be inserted the file "normative.inc"]

Informative references

[Here will be inserted the file "informative.inc"]