Cascading Style Sheets (CSS) Working Group Charter

Scope

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:

• A syntax for associating information with elements in a structured resource, in particular HTML and SVG documents. The main part of the syntax consists of rules that associate properties + values with selectors where the selectors are expressions that match elements in the structured document, based on their position in the document or based on other information about the elements (their type, what the user has done with them, etc.)
• A processing model, referred to as “cascading and inheritance,” that ensures that, given one or more style sheets and a structured document, each element in the document is associated with the full set of properties and values, no matter how short the style sheets or how long the document.
• A rendering model, part of which is a model of typography, i.e., a layout model for text documents, possibly with embedded other objects and possibly involving several documents simultaneously. The model describes blocks and lines of text, characters, columns, colors, dynamic effects, etc. Another part is rendering to speech. It also includes the presentation and behavior of UI widgets. CSS's influence over UI controls is limited to defining shortcut keys, the look of controls in various states during interaction (valid/invalid, required, inactive, etc.), hiding/unhiding, and other local behaviors, but CSS does not itself change the state of elements and does not define how (form) elements interact with a server. (The general principle is that CSS can enhance the user's interaction with a document, but the document is functional without it.)
• The CSS Object Model, a set of standard APIs, to which libraries can be written for manipulating style sheets and documents with associated style information.

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.

• Production of stable documents addressing the work items listed in the Deliverables section.
• Test suites for each deliverable with conformance criteria.
• Availability of multiple, independent, interoperable implementations of each feature with conformance criteria in each deliverable; as demonstrated by an implementation report (summarizing implementation status against the relevant test suite) for each testable class of product, including user agents.
• Deployment on multiple types of platform (traditional computers, phones, tablets, accessibility aids, print formatters, and so on).
• User community and industry adoption of the group deliverables.