Kevin Davis has been creating weblog "themes" using XML/XSLT/CSS:
The showcased XML document is linked to an XSLT (extensible stylesheet language tranformations) document. This document reads the XML data and transforms it into something that a web browser (in our case, IE6, Netscape 6+, Mozilla) can read. In turn, the XSLT document is linked to a CSS (cascading style-sheet) document which defines font-sizes, background images and other superficial (but important) styling.
Kevin shows us a future in which Movable Type outputs standard XML templates, which users may then link to a central repository of themes. In a best case scenario, novice webloggers are able to effortlessly render their site using widely available, semantically correct, standards compliant, and, we'd hope, attractive themes.
To illustrate the power of his project, Keven has created copies of his CSS Zen Garden entry and Dave Shea's mezzoblue.com using identical XML documents.
Jon Hicks notes in a comment to Kevin's site that this project makes him feel like a "silent movie actor with the talkies about to come." We know what he means.
Also: Those interested in following Kevin's lead should read Carey Evans's notes on getting Mozilla to display escaped content.