Including a DTD in a <source> element should be ignored. But the PATTERN_DOCTYPE regular expresion used in the validate() method in AbstractXmlParser finds this and results in the XML being validated and causes a SAXParseException.
This is causing
MSITE-464 reported against the maven-site-plugin.
We're also seeing a similar problem with the maven-pmd-plugin which may be related.
Attaching a test case which demonstrates this.