- From: Sally Khudairi <khudairi@w3.org>
- Date: Tue, 12 May 1998 14:58:17 -0400
- To: w3c-news@w3.org
Contact
America --
Sally Khudairi <khudairi@w3.org>
+1.617.253.8036
Ian Jacobs <jacobs@w3.org>
+1.212.874.4716
Contact
Europe --
Ned Mitchell <ned@ala.com>
+33 1 43 22 79 56
Andrew Lloyd <allo@ala.com>
+44 127 367 5100
Contact Asia --
Yumiko Matsubara
<matsubara@w3.org>
+81 466.49.1170
CSS gives content creators, designers and readers
the power tools they need to realize the full potential
of the their HTML and XML documents. CSS2
includes all the power of CSS1, and adds
enhancements in several areas to make the Web
more appealing for both content providers and users.
The CSS2 Recommendation is based upon CSS1, a
W3C Recommendation issued in December 1996, and
is a prerequisite for the Document Object Model
(DOM), W3C's platform- and language-neutral
interface, which allows programs and scripts to
dynamically access and update the content, structure,
and style of documents.
The CSS2 specification has been produced as part of
the W3C Style Activity. For further information about
CSS, see http://www.w3.org/Style/css/
Improved design capabilities
CSS2 offers precise control over the presentation of
Web pages. The ability to position elements explicitly
greatly enhances control of document layout, both on
screen and in print. Relatively positioned elements are
shifted, by an amount specified by the designer, from
the position they would have occupied in normal flow.
Absolutely positioned elements are taken out of the
normal flow of text entirely, and can be placed
elsewhere to create navigation bars, indexes, and
similar features. Floated elements can be used to
place text or graphics in the margins, with text flowing
around the floated element.
CSS2 has a rich WebFonts capability, offering
dynamic download of fonts from a Web site (just as
images are downloaded today). The fonts can be
locked to a particular Web site and are not installed on
the client machines. WebFonts also includes the
information needed to synthesize fonts or to select
similar looking fonts on the client, if the fonts specified
by the designer are not available.
CSS selectors, which determine what style rules are
applied to which parts of the document, have been
made more powerful in CSS2. This gives designers
greater flexibility and expressive power, particularly
when styling XML documents.
Fast and maintainable sites
Prior to style sheets, the markup needed to simulate
common typographic effects such as exdented
headings, wide margins, and drop capitals caused
documents to bloat and tied them to a single style of
presentation. For example, without style sheets, to
make all headings appear in a particular font, extra
markup must be placed around every single heading
in the document. It is easy to miss one heading, giving
an inconsistent look. Redesigning such a document
implies changing all of the tags.
"Consolidating all the presentation information into
one part of the document, and not having to repeat it,
makes the document shorter and simpler to edit,"
explained Chris Lilley, chair of the CSS&FP working
group that produced CSS2. "Moving it into a separate
style sheet is even better, allowing re-use and easing
maintenance."
The separation of style and content allows a single
style sheet to define the style for a group of related
Web pages, or even an entire Web site. The result is
shorter documents, which in turn, load faster. Once
the first document has loaded, the rest are even faster
because the browser need only fetch the style sheet
once. A recent W3C study showed that using CSS
with W3C's Portable Network Graphics (PNG) and
HTTP/1.1 can dramatically reduce page download
times and ease the load on the global Internet.
Write once, read anywhere
CSS2 introduces the concept of named media.
Portions of a style sheet can be marked as only
applying to certain media. For example, one part of a
style sheet can set colors just for the screen, one part
can set margins for when the page is printed, and the
rest can specify what is common to both screen and
print media.
Audio presentation of Web content -- using speech
synthesis -- is an attractive alternative for accessing
information, particularly suitable for home
entertainment, industrial and medical information
systems, and in-car browsers. CSS2 allows designers
to control how HTML and XML documents are
spoken, including the volume, speed, stress, and
richness of the computer generated voices. The
stereo position of voices, audio clips, and background
music can also be controlled with CSS2.
Accessible to all
Besides the significant increase in accessibility of
Web pages that use style sheets, CSS2 includes a
number of specific features that improve accessibility.
Users, as well as document authors, can specify style
sheets; these are cascaded together to produce the
end result. User style sheets can range from simple
(e.g., increasing the overall size of the text) to complex
(e.g., specifying full aural rendering). The ability to
select elements with particular attributes and to
generate content allows users to specify that, for
example, alternate text ("alt" text) or titles on images
should be displayed. Auto numbering of headings can
also be a useful navigation aid.
Internationalization
Continuing the W3C goal of ensuring a truly World
Wide Web, the members of the W3C CSS&FP
Working Group drew on the experience of leading
experts on internationalization and fonts. To
accommodate internationalization, CSS2 fully supports
the international ISO 10646 character set, allowing
authors to manage differences in language, text
direction, and character encoding schemes. CSS2 can
display left-to-right, right-to-left, or mixed text such as
a Hebrew document, containing a French quote,
which itself contains a phrase in Arabic.
CSS2 enables document authors to apply specialized
formatting to portions of documents depending on the
language in which they are written. Font sets can be
constructed to display multilingual documents. CSS2
extends list numbering to allow additional international
styles. In addition, CSS2, when coupled with
internationalization features, makes it easier to seach
through content.
The CSS2 Package
The CSS2 Recommendation is supported by the W3C
CSS2 Package, consisting of the CSS2 Validation
Service, a set of W3C Core Style Sheets, and the
CSS Test Suite. The CSS2 Package will help
document authors use CSS2 and also help
developers create CSS2-compliant software.
W3C CSS2 Validation Service
Today, W3C expanded its HTML Validation Service to
include full CSS validation (both levels 1 and 2) at
http://jigsaw.w3.org/css-validator. Content providers
can be sure their style sheets are valid, either by
giving the Web address or by pasting the style sheet
into a form.
The service outputs error and warning messages,
suggests style sheet improvements, and formats the
corrected style sheets so they are easy to read.
"Browsers silently ignore style sheet errors, doing
their best to work around errors," said Bert Bos,
co-architect of CSS and one of the editors of the
CSS2 Recommendation. "That's good for the user but
doesn't help authors correct bugs. The best way to
know whether your style sheets are correct is to run
them by the CSS Validation Service."
W3C CSS Core Style Sheets
The Core Style Project proposes a modular
architecture for Web style sheets. It builds upon the
CSS1 Base Style Sheet incorporated into the CSS2
Recommendation. The project aims to promote
cascadability among Web style sheets of diverse
origins by providing style authors with generic, yet
attractive models and bases for their own elaboration.
Shared CSS style sheets offer benefits to Web site
developers, content providers, and users alike. Style
sheet reuse means less site management and more
consistent appearance. Consistency sends a strong
message about corporate identity. It also improves
accessibility by making it easier to navigate the site.
Shared styles free content providers from the burden
of rewriting style rules for each document. The
cascade gives them the best of both worlds: reuse
and extensibility.
"With CSS2 and the Core Styles," said Todd Fahrner,
the Studio Verso designer behind the Core Style
Sheets, "CSS moves beyond the 'good idea' phase
and becomes a critical element of a new, more
attractive and manageable Web, where substance
and style complement one another as peers."
The W3C Core Style Sheets page
(http://www.w3.org/StyleSheets/Core/) explains how to
link to the style sheets and provides samples that
illustrate the effects of the Core Styles. W3C will
continue to add to these Core Styles and intends to
make css.w3.org a gallery of style sheets contributed
by Web designers for communal consumption.
W3C CSS Test Suite
To ensure that pages designed with CSS work best
on any browser, W3C is releasing a reference suite of
CSS test documents
(http://www.w3.org/Style/CSS/Test).
"The W3C CSS Test Suite is a tool for implementors
to ensure interoperability with other CSS-based
software," said Eric Meyer of Case Western Reserve
University, who is coordinating the test suite efforts.
"Key contributions from Tim Boland of NIST, W3C
and the Web community have produced a test suite
that covers all of CSS1". The Test Suite will be
completed with CSS2 test documents in the near
future.
Implementors can conduct tests on their CSS clients
(authoring tools, browsers, format converters, etc.) by
reading test suite documents and verifying the results
against the expected rendering described in the test
suite.
W3C Recommendation Process
Specifications developed within W3C working groups
must be formally approved by the Membership.
Consensus is reached after a specification has
proceeded through the following review stages:
Working Draft, Proposed Recommendation, and
Recommendation.
Working Drafts are written by a Working Group, who
typically meet by teleconference every week and also
meet in person four to six times a year. Once stable,
working drafts are submitted by working groups to the
W3C Director for consideration as a Proposed
Recommendation. Upon the Director's approval, the
document becomes a Proposed Recommendation and
is forwarded to the W3C Membership, who votes
whether it should become an official W3C
Recommendation. The W3C Advisory Committee --
comprised of one official representative from each
Member organization -- submits one of the following
votes on the Proposed Recommendation: yes; yes,
with comments; no, unless specified deficiencies are
corrected; no, this Proposed Recommendation should
be abandoned.
During the Member review and voting period
(approximately 6 weeks), the Working Group resolves
minor technical issues (if any) and communicates its
results to the W3C Director. After this time, the
Director announces the disposition of the document; it
may become a W3C Recommendation (possibly with
minor changes), revert to Working Draft status, or may
be dropped as a W3C work item.
Received on Tuesday, 12 May 1998 14:58:19 UTC