harm_game_rule_enablement_trigger

harm_game_rule_enablement_trigger = {
	# Disable entirely if harm_safe.
	switch = {
		trigger = has_game_rule
		harm_safe = {
			always = no
		}
		harm_target_player_only = {
			is_ai = no
		}
		harm_target_ai_only = {
			is_ai = yes
		}
		fallback = {
			always = yes
		}
	}
	# Never just kill the player if it'd utterly game-over them.
	trigger_if = {
		limit = { is_ai = no }
		# Either because they have no heir.
		exists = player_heir
		# Or because they have an heir they can't survive with.
		player_heir.dynasty ?= dynasty
	}
	# Immortals do not receive harm events, as they would be inevitably killed by them over a long enough period of time.
	NOT = { has_trait_with_flag = is_immortal }
}

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