The Filter interface defines the behaviors supported by objects
which encapsulate constraints used by the proxy objects associated
with an event channel in order to determine which events they
receive will be forwarded, and which will be discarded.
If the intended child poa is not found and activate_it is TRUE,
it is possible for another thread to create the same poa with
create_POA at the same time in a race condition.
Put the (real) parse stack into error recovery configuration by
popping the stack down to a state that can shift on the special
error symbol, then doing the shift.