Can somebody step me through perk books ?

[Atrophied]

I'm looking into creating a few perk books to unlock parts crafting for players.

I've been poking through the code but can't figure out the perk book structure, how they're made, defined and unlock recipes, all i see is a mess of code.

 

I know I'll have to create a few recipes, that part is easy enough but I can't seem to find anything I recognize as the books themselves in items or any other files and only references in progression.xml.

 

EDIT:

I found it