Before revision: There are two main requirements: when functional, to never allow an invalid signals to penetrate the energy barrier, and to never fail in a way that can pass a signal though the barrier before the weak links inside the exclusion zone have also failed.
After revision: There are two main requirements: when functional, never to allow an invalid signals to penetrate the energy barrier, and never to fail in a way that can pass a signal though the barrier before the weak links inside the exclusion zone have also failed.