bp2_valid_to_offer_as_hostage_trigger

bp2_valid_to_offer_as_hostage_trigger = {
	# Update if this is changed : offer_hostage_interaction_desc

	# Must not be a hostage already
	is_hostage = no
	# Cannot send self as hostage
	NOT = { this = $SENDER$ }
	# Must be under sender's control
	liege ?= $SENDER$
	# Hostages must be landless and not a ruler
	is_landed = no
	is_landless_ruler = no
	is_married = no
	is_betrothed = no
	# If imprisoned, it must be by sender
	trigger_if = {
		limit = { is_imprisoned = yes }
		imprisoner = $SENDER$
	}
	# Hostages must be very close relations of sender
	OR = {
		is_child_of = $SENDER$
		is_grandchild_of = $SENDER$
		is_sibling_of = $SENDER$
		is_nibling_of = $SENDER$
	}
	# Not already offered and travelling
	NOR = {
		exists = var:hostage_travelling_to_warden
		exists = var:guardian_travelling_to_ward
		exists = var:ward_travelling_to_guardian
	}
	# You can't send your diarch away as a hostage.
	custom_tooltip = {
		text = hostage_cannot_offer_own_regent_tt
		NOT = { this = $SENDER$.diarch }
	}
	trigger_if = {
		limit = { exists = scope:war }
		scope:war = {
			custom_tooltip = {
				text = hostage_exchange_invalid_for_crusade_tt
				NOR = {
					using_cb = undirected_great_holy_war
					using_cb = directed_great_holy_war
				}
			}
			custom_tooltip = {
				text = hostage_exchange_invalid_for_cb_tt
				bp2_hostage_exchange_invalid_cb_trigger = no
			}
		}
	}
}

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