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InsertableElementsInfo is a simple 'data packet' class that is used to
get information into and out of the validator APIs that allow you to ask
what kind of elements can be inserted into a particular place in an
element's content model.
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.
This class handles the following scenarios:
a
a?
a*
a+
a,b
a|b
These all involve a unary operation with one element type, or a binary
operation with two elements.