||Content model any node.
||Content model Bin-Op node.
||Content model leaf node.
||A content model node.
||This class is a very simple bitset class.
||Content model Uni-Op node.
||DFAContentModel is the derivative of ContentModel that does
all of the non-trivial element content validation.
||MixedContentModel is a derivative of the abstract content model base
class that handles the special case of mixed model elements.
||SimpleContentModel is a derivative of the abstract content model base
class that handles a small set of simple content models that are just
way overkill to give the DFA treatment.