A special Gtk::MenuItem which is used to tear off and reattach its menu.
When its menu is shown normally, the Gtk::TearoffMenuItem is drawn as a dotted line indicating that the menu can be torn off. Activating it causes its menu to be torn off and displayed in its own window. When its menu is shown as a tearoff menu, the Gtk::TearoffMenuItem is drawn as a dotted line which has a left pointing arrow graphic indicating that the tearoff menu can be reattached. Activating it will erase the tearoff menu window.