In one of the first "proper" computing jobs, I had been shown around, and found a temporary desk. I was told that I should try to find out everything I could about the system which I would be working with. I approached my colleagues and asked if they had any detailed documentation - database design documents and so on.
When they had stopped laughing, and realised I was serious they looked at me pityingly and said, "well, the real documentation is the source code. If you really want to know what it's doing, look at the code".
I don't know about the items in about
:config. Probably there are some out of date and incomplete lists out there, but ultimately, looking at the code is the only sure way to know.