Ok, non c'è storia:

from xsl-list mailing archive

codice:
[..]
XSLT 1.0 processors don't do XHTML.  You can have XML (with some
inappropriate element minimizations) or HTML (which is not well-formed).
This is a limitation of the current spec which XSLT 2.0 should correct,
since it will allow for XHTML output.
[...]
Con l'attuale implementazione di XSLT, è possibile generare solamente HTML e non XHTML.

Grazie a tutti! Cyo!