XSL is not the W3C's first style specification; cascading style sheets (CSS) already provides Web developers the ability to separate style from content and apply single style documents to multiple pages.
XSL provides more functionality than CSS, but it is more difficult to master, according to W3C spokesman Ian Jacobs.
"CSS is an easier language to use," Jacobs said. "XSL allows more sophisticated formatting of more complex documents. Complexity gives you both more power and possibly more confusion as well."
XSL's attributes fall into two categories: formatting, which CSS already addresses; and transformation, which CSS does not address.
Formatting has to do with the presentation of content. XSL puts a stronger emphasis than does CSS on formatting in printed documents. For example, XSL will let Web authors determine the placement and style of page numbering regardless of how a printer outputs pages.
XSL also will let authors drill down to control formatting on smaller units of text than does CSS.
Despite the fact that both the XSL and CSS groups are working on formatting, the W3C's Jacobs says the organization will try to avoid creating two different models. Now that the XSL working draft is out, the two working groups have begun a collaborative formatting document, he said.
Transformation concerns the conversion of a document from one XML-based application to another. XSL will describe how to execute that conversion, directing how to take the content from an element in the original application and place it in the next.