marriage_interaction_valid_target_trigger

marriage_interaction_valid_target_trigger = {
	# Clergy cannot marry if their faith doesn't allow it
	trigger_if = {
		limit = {
			scope:secondary_actor = { is_clergy = yes }
		}
		custom_description = {
			text = character_is_clergy_and_cannot_marry
			subject = scope:secondary_actor
			object = scope:secondary_recipient
			scope:secondary_actor = { marriage_clergy_can_marry_trigger = yes }
		}
	}
	trigger_else_if = {
		limit = {
			scope:secondary_recipient = { is_clergy = yes }
		}
		custom_description = {
			text = character_is_clergy_and_cannot_marry
			subject = scope:secondary_recipient
			object = scope:secondary_actor
			scope:secondary_recipient = { marriage_clergy_can_marry_trigger = yes }
		}
	}
	#Marriage
	trigger_else_if = {
		limit = {
			scope:secondary_actor = { is_adult = yes }
			scope:secondary_recipient = { is_adult = yes }
		}
		scope:secondary_actor = {
			custom_description = {
				text = "can_marry_check_secondary_actor"
				subject = scope:secondary_actor
				object = scope:secondary_recipient
				can_marry_character_trigger = { CHARACTER = scope:secondary_recipient } #Checks marriage status, betrothed, gender, consanguinity, faith hostility etc.
			}
		}
	}
	#Betrothal
	trigger_else = {
		scope:secondary_actor = {
			custom_description = {
				text = "can_betroth_check_secondary_actor"
				subject = scope:secondary_actor
				object = scope:secondary_recipient
				can_marry_character_trigger = { CHARACTER = scope:secondary_recipient } #Checks marriage status, betrothed, gender, consanguinity, faith hostility etc.
			}
		}
	}

	# If the actor is ai they will not pick a character already considered for concubinage
	trigger_if = {
		limit = {
			scope:actor = { is_ai = yes }
		}
		NOR = {
			scope:secondary_actor = { has_character_flag = has_been_offered_as_concubine }
			scope:secondary_recipient = { has_character_flag = has_been_offered_as_concubine }
		}
	}
}

As written in game/common/scripted_triggers/00_marriage_triggers.txt.