Setting version="1.0" on the xsl:stylesheet should
prevent all use of extensions defined only in XSLT
1.1. It currently doesn't prevent attributes of
xsl:output being written as attribute value templates.
Applies to Saxon 6.5 only.
(Note, xml:base is also supported regardless of
version. I don't intend to change this, because there
is nothing in XSLT 1.0 that says xml:base must not be