GROUP_CALL_DEFAULT = 0 - Regular group call flag (no flags).
GROUP_CALL_REVERSE = 1 - Call a group in inverse-scene order.
GROUP_CALL_REALTIME = 2 - Call a group immediately (usually calls are delivered on idle).
GROUP_CALL_UNIQUE = 4 - Call a group only once, even if call is performed many times.
I know you asked this question last year, but I found the answer (maybe you have too).
I’ll post it for other people wondering