I have learned – slowly(!) how to be much more careful when using Dreamweaver – mistakenly saving files in the wrong format (eg html instead of xml) and problems of previewing temporary files in a browser.
I also had a problem with not having the xml info as the very first line in my document:
<?xml version="1.0" encoding="iso-8859-1"?>
… and am wondering where this information will go if xml is part of an HTML document (or part of an XHTML document) …?
I think it may be going a bit too far to try to mix XHTML and XML on the same page. You might want to use XML if you have a set of repeating data which you want to set up on a page and give more information about what the text means by using XML tags.
XHTML is also XML compliant so if you declare your XHTML page to be an XML one you should be able to add XML to it. Why not try it and see.