Bert Bos
First version: 1 July 2002
Last modified: $Date: 2005/07/20 14:12:47 $
Cascading Style Sheets Working Group
The CSS WG develops and maintains the CSS language and related technologies. CSS allows both authors and readers to specify the display or other rendering of a document, such as text in HTML or a graphic in SVG. CSS has several levels, from simple (level 1) to complex (level 3) and several "profiles," describing how CSS applies on different media (TV, handheld, etc.). Levels 1 and 2 are Recommendations, level 3 is currently being developed.
This is the charter for the CSS WG for the period August 2002 to August 2004. It has been approved by the Director on 15 October 2002. The contents are based on the previous charter (2001/2002) [member-only] and on discussions in the WG.
In August 2004 and then in July 2005, the charter has been extended until September 2005.
The goal of the Cascading Style Sheets Working Group ("CSS WG") is to develop level 3 of CSS ("CSS3") and maintain CSS1 & 2.
CSS is the Web's primary style sheet language for specifying the rendering of text documents, in particular those expressed in HTML and XML-based formats. It can also be used to specify portions of the rendering of certain non-text formats, such as SMIL (multimedia) and SVG (vector graphics). The model of text-flow and the set of properties of CSS are also used for XSL, W3C's style language for complex formatting of XML-based document formats. (XSL is developed by a separate WG.) In addition to visual output (screen, print), CSS also contains styling properties for speech output.
The overall goal of the W3C is to make information easy to generate, easy to maintain, and easy to manipulate by machine. The latter goal in particular allows automatic enhancement of information, such as through smart search engines or conversions to other formats (accessibility!). Two of the methods are separation of information types into modules (structure, content, style, timing, linking, etc.) and developing expressive, yet simple formal languages that are a good compromise between readability for humans and for machines. CSS fits well with those goals.
CSS itself is partitioned into further modules, for different media (screen, speech, print, etc.) and platforms of different capabilities (currently levels 1 & 2, this charter aims to develop level 3). The modules are implicit in CSS2. In CSS3 they are being made explicit, with better descriptions of conformance.
CSS3 will add new features w.r.t. CSS2. E.g., it will allow the existing properties to be used in vertical text; and will allow text and links to behave as traditional, rich hypertext, as is possible in other hypertext systems than the Web. But above all it will reorganize the specification with the aim to make CSS easier to implement, use and validate.
Some of the challenges for CSS in the next years will very likely be the styling of interactivity and of non-text documents, as well as rendering models for multimedia (or hybrid) devices. Hybrid rendering can include visual renderings that also make sound and synchronized speech and text output. Properties for interactivity are necessary for form controls, hyperlinks and user interfaces in general. XForms is an example of a format that needs interactivity and layout for controls instead of text.
The CSS-OM (CSS Object Model), which is an API that is part of the DOM and has originally been created by the DOM WG is now being maintained and developed by the CSS WG.
CSS was one of the first Recommendations published by W3C (its development actually started before the birth of the Consortium) and is one of the most popular. However, it is plagued by a history of buggy implementations; a situation that has led W3C to concentrate much more on conformance, not just for CSS, but for all other specifications as well. The most "draconian" outcome of that is the conformance clause of XML, which completely reverses the accepted wisdom up to that time, that producers (generators) are responsible for correctness and that consumers (parsers) should be tolerant.
CSS does not go that far, but it has very precise parsing rules and for some time the WG has been spending as much time developing test suites as working on the specification itself. The CSS WG also issues Candidate Recommendations for its specifications. In this period, which can take from a few weeks to several months, the specification is kept unchanged and implementations are invited and compared, before the specification is submitted to the W3C membership for advice on whether to make it into a Recommendation.
The year 2000 has been the year that CSS1 implementations matured. The focus is now on CSS2. Several browsers that have come out during 2000 and 2001 have substantial CSS2 support. That enables the WG to work on CSS3, but also requires attention to the interoperability of CSS2. The WG is in the process of publishing a revised version of CSS2, nicknamed "CSS 2.1," that contains all features of CSS (levels 1, 2 and even small parts of 3) that should be widely and correctly implemented in many programs, including desktop browsers for HTML and generic XML, by the end of 2002.
The work of the WG includes analyzing and, if necessary, specifying in CSS3, the following:
For most of the above, drafts already exist, e.g.: more properties for styling form controls and the effects of user interaction; properties for line breaks, hyphenation and justification in non-western text; new selectors, including support for XML Namespaces; multi-column layout; color profiles; running headers & footers in paged presentations; and mathematics. A public "road map" has descriptions of the planned modules and links to published drafts. The Selectors module is already in CR (Candidate Recommendation) phase as of July 2002.
In addition, the WG will:
An example of such coordination is the "color" module of CSS3, which contains features (such as color spaces and transparency) that have originally been developed for SVG and will now be available for all formats that use CSS.
The CSS Working Group has coordinated with other groups in the past whose charters overlapped with presentation and user interface, and worked hard to develop compatible formatting properties which can be reused across specifications developed by various working groups.
As part of its ongoing coordination efforts, the CSS Working Group will request of any other working group who wishes to introduce new properties or new values to existing properties, that those groups first propose such additions to the CSS working group mailing list <w3c-css-wg@w3.org> and help jointly discuss them there before publishing them in a public working draft.
The WG will publish many specifications, some very small ("Mobile profile," "Backgrounds") and some larger ("CSS 2.1"). The planned publications are in various stages of development at the start of this charter period, from CR ("Media queries," "Selectors"), via WD ("Text," "TV profile") and internal draft ("Borders") to not much yet at all. Here is a list of planned specifications and the date they might become Recommendation:
It is not known exactly how many CRs will be issued for the various modules or when they will be issued, but to reduce the amount of work, the WG will generally wait with publishing a CR until a few, say 4 or 5, modules are ready, and publish a single CR for the set.
The CSS WG participates in the Hypertext Coordination Group and the XML Coordination Group.
CSS3 needs to be coordinated with:
There are several groups outside W3C with which the CSS group maintains contact:
Further, it may be necessary to update the registration of the text/css MIME type with IANA.
The WG is chartered to develop specifications that can be implemented "royalty free," as defined in the W3C note "current patent practice" of January 24, 2002. The WG will follow the procedures described in that note.
The following is a summary of the note. It is provided here for convenience only. The definitive statement of the IPR policy of this working group is the note itself.
All representatives of W3C members and invited experts who participate in the WG must disclose all relevant patents that they know of that are held by them or their organization, or commit to a blanket royalty free license (as defined by the patent practice note) for all patents without naming them.
In case participants disclose patents, they must also provide the licensing terms, and in case those are not royalty free, an ad-hoc committee will be formed, called a Patent Advisory Group (PAG), to determine if the WG needs to be terminated or if there is a workaround.
The disclosed patents and licensing terms will be made public and for easier reference, each specification published by the WG will include a link to those disclosures.
There are two kinds of meetings:
The first face-to-face meeting is scheduled for Aug 27-29, 2002 in Paris (France).
In addition to the phone meetings and face-to-face meeting, the CSS WG communicates via the archived member-only mailing list w3c-css-wg@w3.org.
The archived mailing list w3c-format@w3.org is used for discussions that affect both the XSL and CSS WGs.
The archived mailing list www-style@w3.org is used for public discussion of Style Sheets, and WG members are encouraged to subscribe.
Also, the Group page (member-only) is an important means of communication.
This charter is public.
The Group works by consensus. In the event of failure to achieve consensus, the Group may resort to a vote as described in the Process Document.
Requirements for meeting attendance and timely response are described in the Process Document (version of July 2001). The requirements of IPR disclosure are enhanced as described above. Participation (meetings, reviewing and writing drafts) is expected to consume time equal to 1 day per week on average (0.2 fte).
The chairman and team contact can invite people to participate in the group for one or more meetings. See section "4.3.2 How to join a working group or interest group" in the July 2001 Process Document. The same IPR requirements apply to invited experts as to other participants.
The W3C team will ensure that the mailing lists and Group page are adequately maintained and that public Working Drafts are made available on the Technical Reports page. The W3C team will see to it that minutes are taken at teleconferences and face to face meetings and posted to the Group mailing list and to the Group page.
A W3C team member will provide liaison between non-team document editors and the W3C team; including posting revisions of Working Drafts to the Group page.
W3C team members are expected to adopt the same requirements for meeting attendance and timely response as are required of W3C Members.
Bert Bos (estimated 0.4 fte) will be both W3C Team contact and chairman for the CSS WG, Chris Lilley (estimated 0.05 fte) will be a member.
W3C supports CSS with online information, public talks, a public mailing list (www-style@w3.org), a CSS validator and sample style sheets. W3C also receives a donation from Wisdom in the form of part of a programmer for the CSS validator.