In addition, this feature is only to be used if the appropriate parameter is set in the system. An action could be used to start up a rule-based system, for example. The RHS actions of the rules might themselves include frame operations. Retrieval may involve more than just obtaining the value from the slot. First of all notice that a frame may not even contain the slot being requested, but a higher frame may have that slot with a value.
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.