Subject... let me see...

The best I can do is give some examples. Reasons to use different types of housing would certainly qualify, for exactly the reasons you said. Someone write a massive article about creating new languages. Magic was one, as a broad topic, and then narrowing the focus on several different varieties of magic, their uses, advantages and disadvantages. How to make a realistic planet has arrived a couple of times. Pieces of information on how to create a polytheistic or monotheistic religion, reasons to use certain political and governmental systems.

Basically, little pieces of information that other people can use to make their own worlds more realistic and believable. So, yeah. Subject as in pieces of what it takes to make a world.

But now I have a list, and some of those are actually not used yet. So thank you. This was helpful.