But isn't validation of an XSLT 2.0 stylesheet with a schema for XSLT
1.0 going to generally fail (e.g. if xsl:function is used)?
It depends whether the schema has been written to support
forwards-compatibility mode. The XSLT 1.0 spec says that if version is
anything other than "1.0", unrecognized constructs such as xsl:function must
be silently ignored.
Michael Kay