xsl:include element is always used at the top level of the stylesheet. It has a
href attribute, which is a URL (absolute or relative) of another stylesheet
to be textually included within this one. The top-level elements of the included stylesheet
effectively replace the xsl:include element.
xsl:include may also be used at the top level of the included stylesheet, and so
To customize the way in which the
href attribute is handled, a user-written
URIResolver can be supplied. Note that it is the compile-time
URIResolver that is used,
not the run-time
URIResolver. See also Using XML Catalogs.