# Unofficial W3C Validator FAQ

This is a list of frequently asked questions and answers asked on the www-validator-css@w3.org mailing list.

## What does "`org.xml.sax.SAXException: Please, fix your system identifier (URI) in the DOCTYPE rule.`" mean?

Your XHTML document contains a document type declaration but the system identifier points at some non-W3C URI. Your document probably contains something like this: