The xsl:include element is always used at the top level of the stylesheet. It has a mandatory 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 on recursively.

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.