This base interface allows some kind of "semantic interpretation" to be associated with a particular Token. This makes it easy for Tokens of different types share the same kind of interpretation, which is especially useful when parsing maths input.

Developer Notes

• These are useful when you want to do the same thing over a family of Tokens that don't appear related as far as the Token hierarchy goes.
• I'm not aiming to provide semantics for every token - only when it appears useful.