XML in a Nutshell, 3rd Edition

The Levels of CSS

At the time of this writing, there are several versions of CSS. CSS Level 1 was an early W3C Recommendation from 1996 for HTML only, although the extension to XML was obvious. The CSS Level 1 specification was incomplete and led to inconsistent browser implementations.

The next version, CSS Level 2, added many additional style properties. It also placed XML on an equal footing with HTML. Indeed, CSS Level 2 often works better with XML than with HTML because CSS styles don’t have to interact with any predefined rendering semantics. For the most part, CSS Level 2 is a superset of CSS Level 1. That is, all CSS Level 1 stylesheets are also CSS Level 2 stylesheets that mean pretty much the same thing.

The current version is CSS 2.1. CSS 2.1 adds a few minor values to existing properties—for instance, orange is now recognized as a color—but mostly it removes those features of CSS Level 2 that have not been implemented by browsers. It also corrects a few bugs in the CSS2 specification.

The W3C is now working on CSS Level 3. When complete, it will modularize the CSS specification so software can implement particular subsets of CSS functionality without having to implement everything. For instance, an audio browser could implement audio stylesheets but ignore the visual formatting model. Furthermore, CSS Level 3 adds a number of features to CSS, including multi-column layouts, better support for non-Western languages—such as Arabic and Chinese—XML namespace support, more powerful ...