This package corresponds to Ada.Tags but applied to tagged types which are 'imported' from C++ and correspond to exactly to a C++ Class. GNAT doesn't know about the structure od the C++ dispatch table (Vtable) but always access it through the procedural interface defined below, thus the implementation of this package (the body) can be customized to another C++ compiler without any change in the compiler code itself as long as this procedural interface is respected. Note that Ada.Tags defines a very similar procedural interface to the regular Ada Dispatch Table.