|The xsl:include element is only allowed as a top-level element. The inclusion works at the XML tree level. The resource located
by the href attribute value is parsed as an XML document, and the children of the xsl:stylesheet element in this document
replace the xsl:include element in the including document. The fact that template rules or definitions are included does not
affect the way they are processed. It is an error if a stylesheet directly or indirectly includes itself.
Examples (xslt:xml): Overview