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

In addition to the aforementioned DTD's, there are 2 other ways of describing and validating XML documents are XMLSchema and RelaxNG, both of which may be easier to use and support more features than DTD.