artifact_value_trigger

artifact_value_trigger = {
	trigger_if = {
		limit = {
			exists = $VALUE$
		}
		$VALUE$ >= $MIN$
		$VALUE$ < $MAX$
	}
	trigger_else_if = {
		limit = {
			$MIN$ < 50
		}
		artifact_low_rarity_trigger = yes
	}
	trigger_else_if = {
		limit = {
			$MIN$ >= 50
			$MAX$ < 70
		}
		artifact_medium_rarity_trigger = yes
	}
	trigger_else = {
		artifact_high_rarity_trigger = yes
	}
}

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