All I did was try to write a small set of extension methods to validate whether a given string was valid according to the built-in schema string types and the editor in me comes out and starts nit picking. The W3C Schema docs are very good but sometimes annoyingly ambiguous without a degree in lateral thinking.
Problem #1 : Is "" valid?
Section 3.2.1 says
The ·value space· of string is the set of finite-length sequences of characters (as defined in [XML 1.0 (Second Edition)]) that ·match· the Char production from [XML 1.0 (Second Edition)].
So, is the empty string valid then? Taking...