The following widgets do not have an associated window. If you want to capture events, you'll have to use the EventBox. See the section on the EventBox widget.
Gtk.Alignment Gtk.Arrow Gtk.Bin Gtk.Box Gtk.Button Gtk.CheckButton Gtk.Fixed Gtk.Image Gtk.Label Gtk.MenuItem Gtk.Notebook Gtk.Paned Gtk.RadioButton Gtk.Range Gtk.ScrolledWindow Gtk.Separator Gtk.Table Gtk.Toolbar Gtk.AspectFrame Gtk.Frame Gtk.VBox Gtk.HBox Gtk.VSeparator Gtk.HSeparator