mpo_valid_widow_marrier_trigger

mpo_valid_widow_marrier_trigger = {
	#Is a playable character or primary_heir
	OR = {
		root.primary_heir ?= this
		AND = {
			highest_held_title_tier >= tier_county
			is_playable_character = yes
			OR = {
				#Root is wandering landless
				root = {
					is_ruler = no
					NOT = {
						exists = liege
					}
				}
				#Is root's liege
				root.liege ?= this
				#Is root's top liege
				root.top_liege ?= this
				#root has no primary heir
				NOT = {
					exists = root.primary_heir
				}
				#root's primary heir is not of house
				NOT = {
					exists = root.primary_heir.house
				}
				AND = {
					exists = root.house
					NOT = {
						root.house = root.primary_heir.house
					}
				}
			}
			
		}
	}
	
	OR = {
		has_trait = nomadic_philosophy
		culture = {
			has_cultural_pillar = heritage_mongolic
		}
		culture = {
			has_cultural_pillar = heritage_turkic
		}
		faith.religion = faith:tengri_pagan.religion
	}
	#Can have multiple wives or concubines
	rite = {
		OR = {
			rite_has_doctrine = doctrine_polygamy
			rite_has_doctrine = doctrine_concubines
		}
	}
	is_male = yes
	is_adult = yes
	NOR = {
		has_trait = celibate
		has_trait = eunuch
		has_trait = devoted
	}
	#Has a free slot for a wife or concubine
	OR = {
		allowed_more_spouses = yes
		allowed_more_concubines = yes
	}
	#Can marry the widow
	NOT = {
		relation_with_character_is_incestuous_in_my_rite_trigger = { CHARACTER = scope:widow }
	}
}

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