No documentation on UDT or module creation

There is no documentation i may find on the udt on top of that alot of config are scattered in random non common type name-set. What’s going on here someone please explain… This is very low level so I hope for a good answer.
So far i use my common sense to get by with ubt but something are like just completely missing which i know is there or it’s a ancient comment telling me to go to the file and look.