One difference from connecting versus deriving is that with connecting,
it is possible to use connect_notify() instead of connect() which allows
controlling whether the handler will be called before or after the
default signal handler:
http://library.gnome.org/devel/glibmm/unstable/classGlib_1_1SignalProxy1.html#a1dd40d7c3475124bb78053805fbde3f8