O, thanks, I missed that answer. I found it isn't needed, because
the namespaces are added automatically to the result if I defined
them in the outer xsl:stylesheet element
If you do not specify it, your stylesheet is not xslt anymore. You
wanted to create XSLT from XSLT. Which means that the XSLT namespace
is already bound; always.
If you also use other namespaces in your result document, of course
you will need to specify them too.
-- Abel Braaksma