+/// The AbstractTypeUser class is an interface to be implemented by classes who
+/// could possibly use an abstract type. Abstract types are denoted by the
+/// isAbstract flag set to true in the Type class. These are classes that
+/// contain an Opaque type in their structure somewhere.
+///
+/// Classes must implement this interface so that they may be notified when an
+/// abstract type is resolved. Abstract types may be resolved into more
+/// concrete types through: linking, parsing, and bitcode reading. When this
+/// happens, all of the users of the type must be updated to reference the new,
+/// more concrete type. They are notified through the AbstractTypeUser
+/// interface.
+///
+/// In addition to this, AbstractTypeUsers must keep the use list of the
+/// potentially abstract type that they reference up-to-date. To do this in a
+/// nice, transparent way, the PATypeHandle class is used to hold "Potentially
+/// Abstract Types", and keep the use list of the abstract types up-to-date.
+/// @brief LLVM Abstract Type User Representation