My list of hidden resources with confirmed underlying code is as follows:
Code:
; crusade - hard coded, target for crusades
; jihad - hard coded, target for jihads
; italy - hard coded, specifies region that when upgraded to Large City triggers Marian Reforms, default bodyguard switcher for 'roman' culture factions
; no_pirates - hard coded, prevents slave fleets from spawning, can be toggled off in script
; no_brigands - hard coded, prevents slave armies from spawning, can be toggled off in script
; horde_target - hard coded, target for hordes to settle
It's still not clear to me how (where, when, why) the AI decides to settle a horde. It's definitely not as simple as picking the closest region with horde_target from where the horde spawns. You can have 1 horde_target HR on the entire map, and that won't necessarily be where the AI settles. That HR may be one of several parameters the AI takes into consideration such as settlement level, population, income, garrison, turns distance, etc. It would be nice to know exactly how the AI picks their target and if there's a way to force the AI settle somewhere.