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

See XML DTD on W3 Schools:

An XML document with correct syntax is called "Well Formed".

An XML document validated against a DTD is both "Well Formed" and "Valid".