It requires new functionality in User Agents. Unless there are XSL sheets provided for different media, this may lead to accessibility problems. This note only concerns itself with the last method. The XSL language is still under development. At the time of writing, it is a W3C Working Draft.
All syntax shown here is therefore tentative, and only meant to introduce the concepts.
The bulk of an XSL sheet is a series of pattern-action rules. An author of an XSL sheet selects a suitable set of objects for his task. In principle, when an XML syntax for a data-format already exists, it should be fairly easy to derive an XSL template format from that. The result of applying all matching patterns to a document recursively is a tree of objects. The resulting tree of objects is then interpreted, top-down, according to the definition of each object.