Cascading Style Sheets (CSS) Working Group Charter

The mission of the Cascading Style Sheets (CSS) Working Group, part of the Style Activity, is to develop and maintain CSS.

Join the Cascading Style Sheets (CSS) Working Group.

End date 15 June 2016
Extended to 30 Sept 2016
Confidentiality Proceedings are public
Initial Chairs Daniel Glazman, Peter Linss
Initial Team Contacts
(FTE %: 71)
Bert Bos, Chris Lilley
Usual Meeting Schedule Teleconferences: Weekly
Face-to-face: 3-4 per year


Cascading Style Sheets (CSS) is a style sheet language that allows authors and users to attach style (e.g., from fonts and spacing to filter effects and style animations) to structured documents (e.g., HTML documents and XML applications). By separating the presentation style of documents from the content of documents, CSS simplifies Web authoring and site maintenance. It supports media-specific style so that authors may tailor the presentation of their documents to visual browsers, aural devices, printers, braille devices, handheld devices, etc.

The CSS WG develops the following, somewhat independent technologies, all of which are in scope for the CSS Working Group:

An example of a language that uses only the syntax is STTS. An example that uses the syntax, the cascading & inheritance, but not the layout model is the set of properties for styling SVG. CSS levels 1, 2 and 3 include the syntax, cascading & inheritance and rendering model.

CSS is a rather large and complex language. CSS beyond Level 2 is being developed as a set of modules each of which may advance on the W3C Recommendation Track independently. Among them are modules for syntax, cascading and inheritance, and, of course, many aspects of typography, page layout and presentation.

As individual CSS modules advance to REC, the Group periodically publishes a new snapshot of CSS. Each defines the set of CSS modules that are stable at that point.

Profiles are subsets of the features of CSS, usually for a specific kind of device. The CSS WG has published profiles for TV, mobile phones and low-end printers. The number of such profiles should stay as small as possible, but when needed, the working group tries to cooperate with the organizations that need the profiles.

The CSS WG not only develops CSS, but also checks that properties needed by other working groups and which could occur in a style sheet together with CSS properties, are compatible with CSS in general and consistent in their naming schemes. This affects properties such as those of SVG and Device Independence (such as media features), but not properties such as those in STTS nor the presentation attributes of XSL, SVG or DFXP.

Part of the work of the working group is also to develop test suites for the various specifications it publishes.

Another part is to maintain errata and, when needed, publish revised versions of the various specifications.

Success Criteria

The CSS Working Group's work is considered a success if there are multiple independent complete and interoperable implementations of its deliverables that are widely used.


The following is a list of specifications that the WG has worked on in the past and is likely to work on again in this charter period, depending on demand and available resources. This list is not exclusive: The WG may also create new specifications, within its scope. Also, it may split or merge documents.

W3C staff maintains a public list of CSS-related documents and recent changes. Please, see that list for the current activities of the WG.

Active Development

Documents under active development have one or more active editors, regular publication, and test suites in development. They are expected to progress on the Recommendation track during the charter period.


Documents in this category may be progressed, as resources permit.

Completed Work

Errata are collected for documents in this category. If needed (errata are numerous or lengthy), a new edition may be published.


Documents in this category are without active editor, or blocked on outstanding and unresolvable problems, or have no developer interest. They are unlikely to progress in this charter period.

Other Deliverables

The Group creates a comprehensive test suite for each CSS module before it becomes Recommendation.

The group will create an automatic, up-to-date, index of all properties, with each property linked to the part(s) of the specification(s) that define(s) it.

The Group monitors, tracks, and encourages implementation of CSS, both during Candidate Recommendation and afterwards.

The Group maintains a website, wiki and blog with information about the progress of CSS standardization.


The WG will give priority to specifications that are dependencies of other specifications under development in W3C, such as HTML5 and SVG.

Specification transition estimates (for selected specifications only):

Note: The group will document significant changes from this initial schedule on the CSS roadmap page.
Specification FPWD LC CR PR Rec
CSS Image Values and Replaced Content Module n/a n/a n/a Nov 2014 Dec 2014
CSS Values and Units Module n/a n/a n/a Nov 2014 Dec 2014
CSS Cascading and Inheritance n/a n/a n/a Nov 2014 Dec 2014
CSS Basic User Interface Module n/a Jul 2014 Aug 2014 Mar 2015 Apr 2015
CSS Object Model (CSSOM) n/a Nov 2014 Jan 2015 Aug 2015 Sep 2015
CSSOM View Module n/a Nov 2014 Jan 2015 Aug 2015 Sep 2015
Cascading Style Sheets Level 2 revision 2[PER] n/a n/a n/a May 2014 Jun 2014
CSS Animations n/a Jun 2014 Jul 2014 Mar 2015 Apr 2015
CSS Transitions n/a Jun 2014 Jul 2014 Mar 2015 Apr 2015
CSS Transforms Module n/a Jun 2014 Jul 2014 Mar 2015 Apr 2015
Filter Effects Module n/a Nov 2014 Dec 2014 Jul 2015 Aug 2015
CSS Masking Module n/a n/a May 2014 Jan 2015 Feb 2015
Compositing and Blending n/a n/a May 2014 Jan 2015 Feb 2015

Timeline View Summary

  • 2014-06: LC: CSS Animations
  • 2014-06: LC: CSS Transforms Module Level 1
  • 2014-06: LC: CSS Transitions
  • 2014-06: REC: Cascading Style Sheets Level 2 revision 2
  • 2014-07: CR: CSS Animations
  • 2014-07: CR: CSS Transforms Module Level 1
  • 2014-07: CR: CSS Transitions
  • 2014-07: LC: CSS Basic User Interface Module Level 3
  • 2014-08: CR: CSS Basic User Interface Module Level 3
  • 2014-09: face-to-face meeting
  • 2014-10: face-to-face meeting (TPAC)
  • 2014-11: LC: CSS Object Model (CSSOM)
  • 2014-11: LC: CSSOM View Module
  • 2014-11: LC: Filter Effects Module Level 1
  • 2014-11: PR: CSS Cascading and Inheritance Level 3
  • 2014-11: PR: CSS Image Values and Replaced Content Module Level 3
  • 2014-11: PR: CSS Values and Units Module Level 3
  • 2014-12: CR: Filter Effects Module Level 1
  • 2014-12: REC Image Values and Replaced Content Module Level 3
  • 2014-12: REC: CSS Cascading and Inheritance Level 3
  • 2014-12: REC: CSS Values and Units Module Level 3
  • 2015-01: CR: CSS Object Model (CSSOM)
  • 2015-01: CR: CSSOM View Module
  • 2015-01: PR: CSS Masking Module Level 1
  • 2015-01: PR: Compositing and Blending Level 1
  • 2015-02: REC: CSS Masking Module Level 1
  • 2015-02: REC: Compositing and Blending Level 1
  • 2015-02: face-to-face meeting
  • 2015-03: PR: CSS Animations
  • 2015-03: PR: CSS Basic User Interface Module Level 3
  • 2015-03: PR: CSS Transforms Module Level 1
  • 2015-03: PR: CSS Transitions
  • 2015-04: REC: CSS Animations
  • 2015-04: REC: CSS Basic User Interface Module Level 3
  • 2015-04: REC: CSS Transforms Module Level 1
  • 2015-04: REC: CSS Transitions
  • 2015-05: face-to-face meeting
  • 2015-07: PR: Filter Effects Module Level 1
  • 2015-08: PR: CSS Object Model (CSSOM)
  • 2015-08: PR: CSSOM View Module
  • 2015-08: REC: Filter Effects Module Level 1
  • 2015-09: REC: CSS Object Model (CSSOM)
  • 2015-09: REC: CSSOM View Module
  • 2015-09: face-to-face meeting
  • 2015-10: face-to-face meeting (TPAC)

Dependencies and Liaisons

W3C Groups

WAI Protocols and Formats Working Group
The Group coordinates closely with WAI PF to ensure effective support for accessibility.
Independent User Interface (Indie UI) Working Group
The Group coordinates with Indie UI on styling-related aspects of device independent user interfaces.
Internationalization Activity
The Group coordinates closely with the Internationalization Activity to ensure effective support for internationalization.
Privacy Interest Group
Style sheets can depend on client-side information (e.g., whether a link has been visited before, or the size of the screen) and may leak such information to a remote server, especially if the client also implements a scripting language. The group consults privacy and security experts for workarounds and guidelines.
Web Application Security Working Group
For the same reason, the group also coordinates with the WebAppSec WG, which, among other things, develops the Content Security Policy (CSP) specification (which aims to protect against a man-in-the-middle attacker changing a style sheet). Also, the Cross-Origin Resource Sharing (CORS) specification of the WebAppSec WG is re-used by CSS for WOFF fonts (although not for security, but to flag a certain kind of copyright license).
Scalable Vector Graphics (SVG) Working Group
The Group coordinates closely with the SVG WG on common features (such as the CSS Animations, CSS Fonts, CSS Object Model, CSS 2D and 3D Transformations, and CSS Transitions Modules) to meet the needs of HTML/CSS, SVG, and mixed HTML/CSS/SVG content, and to ensure compatibility at the functionality level for ease of implementation and authoring. The FX Task Force is the primary venue for this work, and those specifications are published jointly.
The CSS WG is aware of normative references to CSS specifications from SVG and will endeavor to maintain their stability, for example by avoiding breaking changes to the referenced portions.
Web Applications Working Group
The Group reviews the Selectors API specification, being developed by the WebApps WG.
WebFonts Working Group
The Group coordinates with the WebFonts WG to enable high quality Web typography with downloadable fonts, in particular WOFF.
Digital Publishing Interest Group
The group coordinates closely with the DPub IG on requirements for various aspects of CSS in all types of digital publishing, including for e-books and publications on paper.
HTML Working Group
The group coordinates with the HTML WG to ensure that HTML only contains constructs that can be rendered with CSS.
The CSS WG is aware of normative references to CSS specifications from HTML5 and will endeavor to maintain their stability, for example by avoiding breaking changes to the referenced portions.
Math Working Group
The group coordinates with the Math WG to ensure CSS can style mathematical formulas (e.g., when formulas are mixed with text in HTML).

Furthermore, Cascading Style Sheets (CSS) Working Group expects to follow these W3C Recommendations:

External Groups

The International Digital Publishing Forum (IDPF)
The Group liaises with the IPDF, who develop the EPUB standards for eBooks, to ensure interoperability and convergence between Web and eBooks in the area of styling.


To be successful, the group is expected to have 25 or more active participants for its duration. Effective participation is expected to consume a minimum of one work day per week for each participant; two days per week for editors. The group allocates also the necessary resources for building Test Suites.

Participants are reminded of the Good Standing requirements of the W3C Process.


The Group holds weekly teleconferences, and primarily conducts its work on the public mailing list www-style@w3.org (archive) for technical discussions. A member-only mailing list w3c-css-wg@w3.org (archive) is also available for member-only communications

The list of current members of the CSS WG is public.

Information about the group (deliverables, participants, face-to-face meetings, teleconferences, etc.) is available from the CSS Working Group page and the CSS Working Group wiki.

Decision Policy

As explained in the Process Document (section 3.3), this group seeks to make decisions when there is consensus. When the Chair puts a question and observes dissent, after due consideration of different opinions, the Chair should record a decision (possibly after a formal vote) and any objections, and move on.

Decisions are made by consensus of the Working Group. In addition to decisions made on teleconferences or face to face meetings, decisions may also be made by a call for consensus on the public mailing list; consensus to be determined by the chairs after some reasonable interval for objections. This avoids waiting for the next weekly call, if consensus can be determined before then.

Patent Policy

This Working Group operates under the W3C Patent Policy (5 February 2004 Version). To promote the widest adoption of Web standards, W3C seeks to issue Recommendations that can be implemented, according to this policy, on a Royalty-Free basis.

For more information about disclosure obligations for this group, please see the W3C Patent Policy Implementation.


Changes since the draft charter sent for AC review to take into account comments received are:

  • The terms "High priority", "Medium priority" and "Low Priority" to classify deliverables were removed. New terms indicate whether specifications are being actively developed or not.
  • Deliverables were sorted alphabetically, and inconsistent level/version numbers removed. A duplicate module was removed, and changes due to module merges taken into account. Two missing modules (now published to /TR) were added.
  • Encouraged use of call for consensus.
  • A reminder, duplicating the W3C Process Document on Formal Votes, was removed as the Process document discourages use of formal voting.
  • Explained what CSS actually is.
  • The addition of this changes section.

Changes to the current charter:

About this Charter

This charter for the Cascading Style Sheets (CSS) Working Group has been created according to section 6.2 of the Process Document. In the event of a conflict between this document or the provisions of any charter and the W3C Process, the W3C Process shall take precedence.

Please also see the previous charter for this group.

Bert Bos, Chris Lilley

$Date: 2016/07/12 19:02:00 $