  I have had recent reason to do research into XML-based markup languages that are used to create forms for user-interaction. Included are XAML, myXAML, XUL, ZULU, and many others. The ones I mention above all have something in common - they evolved to meet specific needs . As such, they have not had much thought put into them other than what was necessary to make them work. One that does appear to have had a of thought, is urlLink XForms . This is a recommendation of w3.org, and tackles many issues that the others don't.
Specifically, it allows for the idea of re-using the form in different devices, such as PDAs, phones etc. In addition, it extends and builds upon other well-thought out standards, such as XHTML. I think that I should focus my browser efforts on XHTML with support for XForms. If I decide to render other versions of HTML, I can write pre-processors to render those in terms of XHTML. 
