xml-stylesheet or <style>

Hello,

As far as I can tell, there is two possibilities for specifying a CSS for an 
XHTML document; via the (application) mechanism html/head/{style,link}; and 
via the XML processing instruction xml-stylesheet. The former works only for 
XHTML, while the latter works for any XML application.

When in the need of associating a CSS with an XHTML document, what is the best 
method? What differs them apart? Does it matter?

I can understand that the difference is significant when an XSLT is 
specified(if that even works if it's not in xml-stylesheet), since it's on a 
lower level.


Cheers,

		Frans