bp2_valid_hostage_exchange_action_trigger

bp2_valid_hostage_exchange_action_trigger = {
	# Context checks, e.g. alliance
	bp2_valid_hostage_action_shared_trigger = yes
	save_temporary_scope_as = home_court
	# Must be at least some threat for an Exchange to be relevant
	#current_strength_with_allies_value >= root.current_strength_with_allies_fifty_percent_value
	NOR = {
		# Don't already have their hostage
		any_warden_hostage = { home_court = root }
		# Don't already have your hostage
		any_home_court_hostage = { warden = root }
	}
	# Ensure a viable target exists
	any_close_family_member = {
		count >= 1
		bp2_valid_to_offer_as_hostage_trigger = { SENDER = scope:home_court }
		save_temporary_scope_as = their_hostage
	}
	root = {
		# Why Exchange when you could Demand?
		NOT = {
			is_character_interaction_potentially_accepted = {
				interaction = demand_hostage_interaction
				recipient = scope:home_court
				secondary_recipient = scope:their_hostage
			}
		}
		any_close_family_member = {
			bp2_valid_to_offer_as_hostage_trigger = { SENDER = root }
			save_temporary_scope_as = my_hostage
		}
		# Ensure Exchange might be accepted
		is_character_interaction_potentially_accepted = {
			interaction = exchange_hostage_interaction
			recipient = scope:home_court
			secondary_recipient = scope:their_hostage
			secondary_actor = scope:my_hostage
		}
	}
}

As written in game/common/scripted_triggers/05_bp2_hostage_triggers.txt.