3.5 Parser

Sorry if this has been asked before but after about an hour of scouring the forum couldn't find quite what I was looking for.

I'm building a reference library in FGU for a campaign I'm building and want to automate/rework some of the automation in the ruleset for it. Where would I find how the ruleset is parsing information for adding weapon proficiencies for example to the character sheet. I will say I think I found part of it but I feel like its maybe spread out somehow, idk. The way it seems to function versus what I'm finding doesn't quite seem to balance in my head. Any help would be appreciated as it would save me a lot of typing I'm sure lol.