For people to comprehend, it is not sufficient to convey definitions and interfaces. Rather, we need to feel for it.
In modern practice such as OOP, it is all about definitions and interfaces and delieberately hide details (abstractions) from readers (including selves).
The idea behind MyDef is to make details accessible. A "subcode" is simply authentic code with no extra interface, so we see the code as real as it gets -- what we see is all out there -- no guesswork, we feel all of it. After we comprehended the code -- knows it somewhat intuitively -- we may refer to it simply by a name. That is exactly what MyDef let's you do.