Validating an XSL-FO Document
As with any XML documents that you create, it's important to be able to validate XSL-FO documents to ensure that they are coded properly according to the XSL-FO language. The W3C doesn't offer an official XSL-FO DTD, which is necessary in order to validate XSL-FO documents. However, RenderX, the makers of the XEP XSL-FO processor, offer an experimental DTD that works fine for validating XSL-FO documents. Relying on RenderX's DTD, you can still use the standard W3C online validation tool to validate your XSL-FO documents. But first you need to wire the RenderX DTD to your XSL-FO documents.
The RenderX XSL-FO DTD is located online at http://xep.xattic.com/xep/resources/validators/dtd/fo.dtd. You wire this DTD into your XSL-FO documents via the following line of code just after the XML processor directive near the top of a document:
<!DOCTYPE fo:root SYSTEM "http://xep.xattic.com/xep/resources/validators/dtd/fo.dtd">
With this code in place, you can now pass your XSL-FO documents into the standard W3C Markup Validation Service at http://validator.w3.org/.