Windows may seem to be the only operating system on the modern PC and most programming is done for the Windows/Intel platform simply because of the size of the market for those programs. Yet the strength of Microsoft Windows, from v3 to 2000, lies in the desktop PC - a standalone computer with all the processing and storage performed locally. The internet is essentially an add on. Microsoft is now planning a new direction where all computing activities will take place over the internet and local machines will not need software upgrades but will use Windows .NET to access rented services online.
XML is to be the carrier for this new direction for Windows, not HTML. Microsoft's IE5 is currently the only browser to implement XSL - the transformational technology within XML - which is currently able to format XML into HTML and DHTML. Developments in this area could lead to XSL being available to designers of WML (although file size issues still need to be resolved).
XML/XSL can also be implemented to communicate with other non-PC smart devices by transforming the basic XML data into an XML based language suitable for each device. Microsoft hopes to give users a truly integrated experience with seamless exchange of information between your PC, internet sources and smart devices like handhelds, mobiles, databanks or embedded systems.
A note about XML, standards and browsers
The CodeHelp site uses XSL - eXtensible Stylesheet Language which is a transformational language, not a formatting language like CSS. Microsoft Internet Explorer 5 uses formatting with XSL. CodeHelp uses links both to a CSS and an XSL stylesheet, IE picks the XSL version. Other XML capable browsers (like Opera4) only use the CSS stylesheet. XSL is a W3C standard which comes in two parts - a "transformation language" used for preparing documents for display, and a "formatting object set" that is used for actual visual styling. The formatting object set should still be considered a work in progress. However, the transformation language is the main use of XML within the CodeHelp site.
Within the CodeHelp site, the main difference between XML with CSS and XML with XSL is the lack of hyperlinks in the CSS version - the CSS cannot transform the XML data into a <a href></a> tag, it can only format the contents of the href, title and descriptive text which the XML contains. Strangely, there is a way of asking IE5 to create a hyperlink in a CSS/XML combination using the html: namespace. However, this appears not to function in Opera.