The "activate" signal is
emitted when the user presses a mouse button while the cursor is over
the widget, or hits the Enter key or
spacebar while the widget is selected, or if the
activate() method has been
called from within the program by the widget, or if the
activate_item() method has
been called from within the program by the widget's parent.
It is also defined as the accelerator signal, so that any accelerator
key associated with the widget will also emit the
"activate".when pressed,
whether the widget is currently selected or not.
On activation, all GtkMenu widgets that are a
part of the cascading selection sequence disappear from the screen,
regardless of whether or not the GtkMenuItem
has its "activate" signal
connected to a function within the program.
