This identifies a switch slot whose slot-down signal will cause this restriction to automatically expire. An administrator sets this so a restriction tied to a hardware module is cleaned up automatically once that slot is signaled down, for example after a module is removed; note the restriction never expires this way if the slot simply never comes up. For example, setting hpFtrCoExpireSlot to 3 causes the restriction to be removed automatically as soon as slot 3 signals down.