How are program objects in QSYS like QUSROBJD able to be called over a
RPC connection? Is there any setup files? In particular what I want
to know is how the error code information (ERRC0100 and others) is
passed into/out of the program and back to the caller. Also RPC calls
that call QSYS programs are able to get an exception thrown if they do
not provide the ERR code parameter. How does this happen?

Thanks!