The XSL/XQuery | Assign XSL:FO command assigns an XSLT stylesheet for transformation to FO to an XML document. The command opens a dialog to let you specify the XSL or XSLT file you want to assign and inserts the required processing instruction into your XML document.
You can make the path of the assigned file relative by clicking the Make Path Relative To check box. You can also select a file via a global resource or a URL (click the Browse button) or a file in one of the open windows in XMLSpy (click the Window button).
Please note: An XML document may have two XSLT files assigned to it: one for standard XSLT transformations, a second for an XSLT transformation to FO.