Is there any difference between 'valid xml' and 'well formed xml'?

Question

I wasn\'t aware of a difference, but a coworker says there is, although he can\'t back it up. What\'s the difference if any?

Answer 1

If XML is confirming to DTD rules then it's a valid XML. If a XML document is conforming to XML rules (all tags started are closed,there is a root element etc)then it's a well formed XML.