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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html lang=en>
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<head>
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<title>Cascading Style Sheets (CSS) Snapshot 2010</title>
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<!-- <link rel="stylesheet" type="text/css" href="default.css"> -->
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<link href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" rel=stylesheet
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type="text/css">
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<body>
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<div class=head> <!--begin-logo-->
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<p><a href="http://www.w3.org/"><img alt=W3C height=48
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src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
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<h1>Cascading Style Sheets (CSS) Snapshot 2010</h1>
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<h2 class="no-num no-toc" id=w3c-working-draft-date>W3C Working Draft 3
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September 2010</h2>
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<dl>
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<dt>This version:
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<dd><a
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href="http://www.w3.org/TR/2010/WD-css-beijing-20100903/">http://www.w3.org/TR/2010/WD-css-beijing-20100903</a>
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<dt>Latest version:
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<dt>Previous versions:
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<dd><a
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href="http://www.w3.org/TR/css-beijing/">http://www.w3.org/TR/css-beijing/</a>
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<dt>Editor:
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<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
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</dl>
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<!--begin-copyright-->
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<p class=copyright><a
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href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
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rel=license>Copyright</a> &copy; 2010 <a
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href="http://www.w3.org/"><acronym title="World Wide Web
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Consortium">W3C</acronym></a><sup>&reg;</sup> (<a
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href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
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of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
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title="European Research Consortium for Informatics and
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Mathematics">ERCIM</acronym></a>, <a
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href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
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href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
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<a
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href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
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and <a
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href="http://www.w3.org/Consortium/Legal/copyright-documents">document
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use</a> rules apply.</p>
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<!--end-copyright-->
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<hr title="Separator for header">
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</div>
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<h2 class="no-num no-toc" id=abstract>Abstract</h2>
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<p>This document collects together into one definition all the specs that
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together form the current state of Cascading Style Sheets (CSS) as of
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2010. The primary audience is CSS implementors, not CSS authors, as this
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definition includes modules by specification stability, not Web browser
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adoption rate.
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<h2 class="no-num no-toc" id=status>Status of this document</h2>
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<!--begin-status-->
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<p><em>This section describes the status of this document at the time of
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its publication. Other documents may supersede this document. A list of
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current W3C publications and the latest revision of this technical report
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can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
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index at http://www.w3.org/TR/.</a></em>
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<p>Publication as a Working Draft does not imply endorsement by the W3C
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Membership. This is a draft document and may be updated, replaced or
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obsoleted by other documents at any time. It is inappropriate to cite this
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document as other than work in progress.
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<p>The (<a
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href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
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mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
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<a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
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for discussion of this specification. When sending e-mail, please put the
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text &#8220;css-beijing&#8221; in the subject, preferably like this:
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&#8220;[<!---->css-beijing<!---->] <em>&hellip;summary of
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comment&hellip;</em>&#8221;
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<p>This document was produced by the <a
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href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
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the <a href="http://www.w3.org/Style/">Style Activity</a>).
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<p>This document was produced by a group operating under the <a
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href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
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2004 W3C Patent Policy</a>. W3C maintains a <a
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href="http://www.w3.org/2004/01/pp-impl/32061/status"
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rel=disclosure>public list of any patent disclosures</a> made in
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connection with the deliverables of the group; that page also includes
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instructions for disclosing a patent. An individual who has actual
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knowledge of a patent which the individual believes contains <a
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href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
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Claim(s)</a> must disclose the information in accordance with <a
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href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
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6 of the W3C Patent Policy</a>.</p>
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<!--end-status-->
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<!--
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<p>This specification is a <strong>Last Call Working Draft</strong>. All
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persons are encouraged to review this document and <strong>send comments
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to the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a>
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mailing list</strong> as described above. The <strong>deadline for
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comments</strong> is <strong>????</strong>.
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-->
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<h2 class="no-num no-toc" id=contents>Table of contents</h2>
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<!--begin-toc-->
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<ul class=toc>
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<li><a href="#intro"><span class=secno>1. </span>Introduction</a>
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<ul class=toc>
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<li><a href="#w3c-process"><span class=secno>1.1. </span>The W3C Process
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and CSS</a>
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</ul>
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<li><a href="#css-levels"><span class=secno>2. </span>CSS Levels</a>
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<ul class=toc>
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<li><a href="#css1"><span class=secno>2.1. </span>CSS Level 1</a>
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<li><a href="#css2"><span class=secno>2.2. </span>CSS Level 2</a>
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<li><a href="#css3"><span class=secno>2.3. </span>CSS Level 3</a>
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</ul>
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<li><a href="#css"><span class=secno>3. </span>Cascading Style Sheets
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Definition</a>
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<ul class=toc>
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<li><a href="#partial"><span class=secno>3.1. </span>Partial
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Implementations</a>
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<li><a href="#profiles"><span class=secno>3.2. </span>CSS Profiles</a>
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<li><a href="#experimental"><span class=secno>3.3. </span>Experimental
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Implementations</a>
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</ul>
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</ul>
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<!--end-toc-->
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<h2 id=intro><span class=secno>1. </span>Introduction</h2>
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<p>When the first CSS specification was published, all of CSS was contained
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in one document that defined CSS Level 1. CSS Level 2 was defined also by
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a single, multi-chapter document. However for CSS beyond Level 2, the CSS
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Working Group chose to adopt a modular approach, where each module defines
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a part of CSS, rather than to define a single monolithic specification.
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This breaks the specification into more manageable chunks and allows more
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immediate, incremental improvement to CSS.
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<p>Since different CSS modules are at different levels of stability, the
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CSS Working Group has chosen to publish this profile to define the current
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scope and state of Cascading Style Sheets as of late 2010. This profile
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includes only specifications that we consider stable <em>and</em> for
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which we have enough implementation experience that we are sure of that
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stability.
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<p>Note that this is not intended to be a CSS Desktop Browser Profile:
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inclusion in this profile is based on feature stability only and not on
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expected use or Web browser adoption. This profile defines CSS in its most
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complete form.
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<p>Note also that although we don't anticipate significant changes to the
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specifications that form this snapshot, their inclusion does are not mean
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they are frozen. The Working Group will continue to address problems as
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they are found in these specs. Implementers should monitor <a
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href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> and/or
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the <a href="http://www.w3.org/blog/CSS">CSS Working Group Blog</a> for
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any resulting changes, corrections, or clarifications.
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<h3 id=w3c-process><span class=secno>1.1. </span>The W3C Process and CSS</h3>
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<p><em>This section is non-normative.</em>
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<p>In the <a href="http://www.w3.org/2005/10/Process-20051014/">W3C
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Process</a>, a Recommendation-track document passes through five levels of
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stability, summarized below:
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<dl style="list-style-type: decimal">
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<dt>Working Draft (WD)
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<dd>Published during the process of drafting the specification, the
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purpose of a public Working Draft is to create a snapshot of the
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specification's current state and to solicit input from the W3C and the
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public. The document is known to be unstable, and is often incomplete.
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<dt>Last Call Working Draft (LC or LCWD)
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<dd>By publishing a Last Call Working Draft, a working group is expressing
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that they consider the spec to be complete and all issues to be resolved.
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Publishing a Last Call Working Draft announces that this specification
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will move toward Candidate Recommendation unless significant issues are
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brought up. The Last Call period is a last chance for others to submit
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issues before the transition to CR.
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<dt>Candidate Recommendation (CR)
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<dd>By publishing a Candidate Recommendation, a working group is
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expressing that have resolved all known issues and they believe the spec
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is ready for implementation.
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<dt>Proposed Recommendation (PR)
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<dd>To exit CR and enter this stage, the spec needs a comprehensive test
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suite and implementation reports proving that every feature in the spec
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is interoperably implemented in at least two shipping implementations.
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Entering the Proposed Recommendation stage signals to the W3C that these
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requirements have been met. Once the W3C officially approves the
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specification, it becomes a Recommendation.
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<dt>Recommendation (REC)
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<dd>This is the final stage. At this point there should need to be no more
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changes.
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</dl>
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<p>In the CSSWG's experience, the recommendation track is not linear. The
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wider review triggered by an LCWD often results in at least another
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working draft, possibly several. More significantly, our experience is
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that many specs enter CR twice, because implementation testing often
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uncovers significant problems in the spec and thus pushes it back to
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working draft. Additionally, fixing even minor problems forces a CR to
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re-enter the Working Draft stage. As a result, although the CSSWG has a
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clear idea of the stability of the CSS specs, it is very difficult for
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someone outside the working group to come to that same understanding based
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on a specification's official status. The CSS Working Group's motivation
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for creating this document is thus to communicate to others our
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understanding of the state of CSS.
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<h2 id=css-levels><span class=secno>2. </span>CSS Levels</h2>
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<p>Cascading Style Sheets does not have versions in the traditional sense;
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instead it has <dfn id=levels>levels</dfn>. Each level of CSS builds on
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the previous, refining definitions and adding features. The feature set of
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each higher level is a superset of any lower level, and the behavior
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allowed for a given feature in a higher level is a subset of that allowed
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in the lower levels. A user agent conforming to a higher level of CSS is
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thus also conformant to all lower levels.
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<h3 id=css1><span class=secno>2.1. </span>CSS Level 1</h3>
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<p>The CSS Working Group considers the <a
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href="http://www.w3.org/TR/2008/REC-CSS1-20080411/">CSS1 specification</a>
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to be obsolete. <dfn id=css-level-1>CSS Level 1</dfn> is defined as all
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the features defined in the CSS1 specification (properties, values,
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at-rules, etc), but using the syntax and definitions in the <a
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href="http://www.w3.org/TR/CSS21/">CSS2.1 specification</a>. <a
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href="http://www.w3.org/TR/css-style-attr/">CSS Styling Attributes Level
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1</a> defines its inclusion in element-specific style attributes.
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<h3 id=css2><span class=secno>2.2. </span>CSS Level 2</h3>
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<p>Although the <a href="http://www.w3.org/TR/2008/REC-CSS2-20080411/">CSS2
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specification</a> is technically a W3C Recommendation, it passed into the
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Recommendation stage before the W3C had defined the Candidate
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Recommendation stage. Over time implementation experience and further
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review has brought to light many problems in the CSS2 specification, so
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instead of expanding an already <a
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href="http://www.w3.org/Style/css2-updates/REC-CSS2-19980512-errata.html">unwieldy
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errata list</a>, the CSS Working Group chose to define <cite>CSS Level 2
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Revision 1</cite> (CSS2.1).
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<p>CSS2.1 is now a Candidate Recommendation&#8212;effectively though not
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officially the same level of stability as CSS2&#8212;and should be
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considered to obsolete the CSS2 Recommendation. In case of any conflict
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between the two specs CSS2.1 contains the definitive definition. Features
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in CSS2 that were dropped from CSS2.1 should be considered to be at the
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Candidate Recommendation stage, but note that many of these have been or
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will be pulled into a CSS Level 3 working draft, in which case that
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specification will, once it reaches CR, obsolete the definitions in CSS2.
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<p>The <a href="http://www.w3.org/TR/CSS21/">CSS2.1 specification</a>
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defines <dfn id=css-level-2>CSS Level 2</dfn> and the <a
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href="http://www.w3.org/TR/css-style-attr/">CSS Styling Attributes Level 1
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specification</a> defines its inclusion in element-specific style
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attributes.
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<h3 id=css3><span class=secno>2.3. </span>CSS Level 3</h3>
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<p><em>This section is non-normative.</em>
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<p>CSS Level 3 builds on CSS Level 2 module by module, using the CSS2.1
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specification as its core. Each module adds functionality and/or replaces
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part of the CSS2.1 specification. The CSS Working Group intends that the
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new CSS modules will not contradict the CSS2.1 specification: only that
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they will add functionality and refine definitions. As each module is
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completed, it will be plugged in to the existing system of CSS2.1 plus
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previously-completed modules.
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<p>From this level on modules are levelled independently: for example
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Selectors Level 4 may well be defined before CSS Line Module Level 3.
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<h2 id=css><span class=secno>3. </span>Cascading Style Sheets Definition</h2>
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<p>As of 2010, <dfn id=cascading-style-sheets-css>Cascading Style Sheets
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(CSS)</dfn> is defined by the following specifications. Each specification
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in this list builds on and possibly modifies the definitions in the
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previous specifications, with the base formed by <cite>CSS Level 2
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Revision 1</cite>. (In other words, CSS is defined as <cite>CSS Level 2
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Revision 1</cite>, modified by <cite>CSS Namespaces</cite>, modified by
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<cite>Selectors Level 3</cite>, etc.) A valid CSS document is one that
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conforms to this definition.
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<ol>
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<li><a href="http://www.w3.org/TR/CSS21/">CSS Level 2 Revision 1</a>
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(including errata)
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<li><a href="http://www.w3.org/TR/css3-mediaqueries/">Media Queries Level
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3</a>
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<li><a href="http://www.w3.org/TR/css-style-attr/">CSS Styling Attributes
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Level 1</a>
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<li><a href="http://www.w3.org/TR/css3-namespace/">CSS Namespaces</a>
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<li><a href="http://www.w3.org/TR/css3-selectors/">Selectors Level 3</a>
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<li><a href="http://www.w3.org/TR/css3-color/">CSS Color Level 3</a>
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</ol>
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<h3 id=partial><span class=secno>3.1. </span>Partial Implementations</h3>
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<p>So that authors can exploit the forward-compatible parsing rules to
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assign fallback values, CSS layout implementations <strong>must</strong>
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treat as invalid (and <a
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href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore as
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appropriate</a>) any at-rules, properties, property values, keywords, and
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other syntactic constructs for which they have no usable level of support.
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In particular, user agents <strong>must not</strong> selectively ignore
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unsupported property values and honor supported values in a single
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multi-value property declaration: if any value is considered invalid (as
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unsupported values must be), CSS requires that the entire declaration be
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ignored.
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<h3 id=profiles><span class=secno>3.2. </span>CSS Profiles</h3>
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<p>Not all implementations will implement all functionality defined in CSS.
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For example, an implementation may choose to implement only the
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functionality required by a CSS Profile. Profiles define a subset of CSS
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considered fundamental for a specific class of CSS implementations. The
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W3C CSS Working Group defines the following CSS profiles:
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<ul>
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<li><a href="http://www.w3.org/TR/css-mobile/">CSS Mobile Profile 2.0</a>
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<li><a href="http://www.w3.org/TR/css-print/">CSS Print Profile 1.0</a>
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<li><a href="http://www.w3.org/TR/css-tv">CSS TV Profile 1.0</a>
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</ul>
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<h3 id=experimental><span class=secno>3.3. </span>Experimental
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Implementations</h3>
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<p>To avoid clashes with future CSS features, the CSS2.1 specification
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reserves a <a
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href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
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syntax</a> for proprietary property and value extensions to CSS. The CSS
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Working Group recommends that experimental implementations of features in
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CSS Working Drafts also use vendor-prefixed property or value names. This
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avoids any incompatibilities with future changes in the draft. Once a
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specification reaches the Candidate Recommendation stage, implementors
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should implement the non-prefixed syntax for any feature they consider to
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be correctly implemented according to spec.

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