move_to_pool_effect

move_to_pool_effect = {
	save_temporary_scope_as = mover
	###TOOLTIP FOR HOST###
	show_as_tooltip = {
		this.host = { remove_courtier_or_guest = scope:mover }
	}

	###MOVE OR FIND FALLBACK DESTINATION###
	if = {
		limit = {
			exists = scope:destination
		}
		set_variable = {
			name = last_visited_ruler
			value = this.host
			days = 3650
		}
		every_traveling_family_member = {
			limit = {
				NOT = { is_in_pool_at = scope:destination }
				is_ruler = no
				trigger_if = {
					limit = {
						exists = scope:mover.host
						is_child_of = scope:mover.host
						is_adult = no
					}
					dynasty != scope:mover.host.dynasty
				}
			}
			hidden_effect = { move_to_pool_at = scope:destination }
		}
	}
}

As written in game/common/scripted_effects/00_courtier_guest_management_effects.txt.