Basically the title, is there documentation on this somewhere? i can’t seem to find it yet 
I mean to sort materials by element, I can’t find documentation on that.
Sorry your question is a little vague are you looking for how you define areas? or are you looking for how you actually layer the materials on one another?
If your looking how to define areas its done by painting texture masks that are used to blend materials layers. To layer the materials on one another you need to use material layer blend functions.
more info can be found here:
If this doesn’t answer your question let me know if you can clarify it a bit more and I’ll see if i can point you in the right direction.
That’s good thank you 
what i wanted to know.