Signal emission is the process whereby GTK runs all handlers for a
specific object and signal.
First, note that the return value from a signal emission is the return
value of the last handler executed. Since event signals are
all of type GTK_RUN_LAST, this will be the default (GTK supplied)
handler, unless you connect with gtk_signal_connect_after().
The way an event (say "button_press_event") is handled, is:
Start with the widget where the event occured.
Emit the generic "event" signal. If that signal handler returns
a value of TRUE, stop all processing.
Otherwise, emit a specific, "button_press_event" signal. If that
returns TRUE, stop all processing.
Otherwise, go to the widget's parent, and repeat the above two
steps.
Continue until some signal handler returns TRUE, or until the
top-level widget is reached.
Some consequences of the above are:
Your handler's return value will have no effect if there is a
default handler, unless you connect with gtk_signal_connect_after().
To prevent the default handler from being run, you need to
connect with gtk_signal_connect() and use
gtk_signal_emit_stop_by_name() - the return value only affects whether
the signal is propagated, not the current emission.