Overrides the class closure (i.e. the default handler) for the
given signal for emissions on instances of @instance_type with
callback @class_handler. @instance_type must be derived from the
type to which the signal belongs.
See g_signal_chain_from_overridden() and
g_signal_chain_from_overridden_handler() for how to chain up to the
parent class closure from inside the overridden one.
Overrides the class closure (i.e. the default handler) for the given signal for emissions on instances of @instance_type with callback @class_handler. @instance_type must be derived from the type to which the signal belongs.
See g_signal_chain_from_overridden() and g_signal_chain_from_overridden_handler() for how to chain up to the parent class closure from inside the overridden one.