The signal accumulator is a special callback function that can be used to collect return values of the various callbacks that are called during a signal emission. The signal accumulator is specified at signal creation time, if it is left NULL, no accumulation of callback return values is performed. The return value of signal emissions is then the value returned by the last callback.
The accumulator function returns whether the signal emission should be aborted. Returning FALSE means to abort the current emission and TRUE is returned for continuation.