Signal invocation hint, see #GSignalInvocationHint.
Accumulator to collect callback return values in, this is the return value of the current signal emission.
A #GValue holding the return value of the signal handler.
Callback data that was specified when creating the signal.
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.