XUL embedded in an XHTML document doesn't appear in the document. The DOM inspector shows the nodes being in the document, but they don't show up. See the URL for a test case.
This is basically "by design", as a note. XUL stuff really does not work outside a XUL document...
Last time I talked to hyatt (about six months ago), he said it should work. Note also that XUL works fine when inserted into an HTML document via XBL, f.e.: http://www.melez.com/mozilla/xul-in-html/test5.html Given that, I don't see why it shouldn't work when included in an XML document.
> Last time I talked to hyatt (about six months ago), he said it should work. Nope. The code is simply not written to do it... > Note also that XUL works fine when inserted into an HTML document via XBL XBL special-cases XUL. See nsXBLContentSink::CreateElement. Perhaps the special-casing should move to nsXMLContentSink?
The XUL content sink is a big booger. We should be keeping whitespace nodes, like we do for every other kind of XML/HTML doc. Yes, I know this involves fixing all of our JS code which assumes there are no whitespace nodes... but it definitely is a goal to have mixed xul/xhtml/mathml/(and SVG as possible), without having to ship the document with an XUL mimetype.