pam_challenge_hof_join_war_trigger

pam_challenge_hof_join_war_trigger = {
	is_ai = yes
	highest_held_title_tier >= tier_county
	NOR = {
		is_participant_in_war = scope:war
		# Don't add vassals of targets
		is_vassal_or_below_of = scope:defender
		is_vassal_or_below_of = scope:attacker
		# Not part of an attacker's realm
		any_liege_or_above = { is_participant_in_war = scope:war }
	}
	OR = {
		# Military Holy Orders always join
		government_has_flag = government_is_military_holy_order
		AND = {
			# Landed rulers join if zealous independents or theocrats, prevent every cardinal and monastic abbot joining
			is_landed = yes
			OR = {
				AND = {
					is_independent_ruler = yes
					# Attackers always join if rite is different, to reward spreading rite
					trigger_if = {
						limit = {
							scope:defender.rite != scope:attacker.rite
							rite = scope:attacker.rite
						}
						always = yes
					}
					# Otherwise attackers/defenders join only if zealous
					trigger_else = {
						ai_zeal >= very_high_positive_ai_value
					}
				}
				government_has_flag = government_is_theocracy
			}
		}
	}
}

As written in game/common/scripted_triggers/pam_antipope_triggers.txt.