Every subordinate frame can inherit that slot. Only execute the first such action that is found. This feature is only to be used if the appropriate parameter is set in the system. Another possible action that can occur when trying to retrieve a non-existent value is that a default value will be returned. Notice that if during an FGET the slot doesn't exist in this frame then the only option one has is to look in the next frame higher.
Actions can be any function.
These variables should be automagically set by the frame operations. It will probably be appropriate to think of both the FGET and the FPUT as recursive functions. That is, if you can't FGET it from this frame then try to FGET it from the frame above. Termination will be caused by reaching the top of the hierarchy, or by obtaining a value. Try an FGET of the LEGS of Fido.