DFAContentModel is the derivative of ContentModel that does all of the non-trivial element content validation. This class does the conversion from the regular expression to the DFA that it then uses in its validation algorithm.

Note: Upstream work insures that this class will never see a content model with PCDATA in it. Any model with PCDATA is 'mixed' and is handled via the MixedContentModel class since mixed models are very constrained in form and easily handled via a special case. This also makes implementation of this class much easier.