relation_with_character_is_incestuous_in_rite_trigger

relation_with_character_is_incestuous_in_rite_trigger = {
	OR = {
		# doctrine_consanguinity_dynastic; not within the same descent group
		AND = {
			$RITE$ = { rite_has_parameter = consanguinity_restricted_dynastic_marriage }
			is_lowborn = no
			$CHARACTER$.dynasty ?= dynasty
		}
		#doctrine_consanguinity_restricted; absolutely no family business
		AND = {
			$RITE$ = { rite_has_parameter = consanguinity_restricted_close_kin_incest }
			is_close_or_extended_family_of = $CHARACTER$ #[parents, children, siblings, grandparents, grandchildren, cousins, uncles, aunts, nephews, nieces]
		}
		#doctrine_consanguinity_cousins; the only acceptable incest is with your cousin
		AND = {
			$RITE$ = { rite_has_parameter = consanguinity_cousins_marriage }
			OR = {
	            is_close_family_of = $CHARACTER$ #[parents, children, siblings, grandparents, grandchildren]
	            is_uncle_or_aunt_of = $CHARACTER$
	            is_nibling_of = $CHARACTER$
	        }
		}
		#doctrine_consanguinity_aunt_nephew_and_uncle_niece; extended family is ok
		AND = {
			$RITE$ = { rite_has_parameter = consanguinity_aunt_nephew_and_uncle_niece_marriage }
			is_close_family_of = $CHARACTER$
		}
		#doctrine_consanguinity_unrestricted; all forms of incest is acceptable
	}
}

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