Just a note: the MIME type does not NEED to be application/xml. There is a big difference here: text/html will tell the browser "Hey, try to render this page. If something doesn't work do your best." 99% of web pages out there do this. application/xml tells the browser "Treat this as XML. If it's not valid, throw an error and quit." Naturally, most people are shying away from this option since one little mistake can make your entire website unusable.
Agreed. However, if you are not sure that every single bit of code in your application produces valid HTML then you are much safer with the text/html MIME type. As for the SGML vs XHTML debate, I'd rather not get into that since the whole thing got a bit religious at this point.
