An XSLT stylesheet may include another XSLT stylesheet using an xsl:include element. The xsl:include element has an href attribute whose value is a URI reference identifying the stylesheet to be included. 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.