code: func (p *Popover) GetDefaultWidget() *Widget {
  	w := C.gtk_popover_get_default_widget(p.native())
  	if w == nil {
  		return nil
  	}
  	return &Widget{glib.InitiallyUnowned{glib.Take(unsafe.Pointer(w))}}
  }
docs: //GtkWidget *
  //gtk_popover_get_default_widget (GtkPopover *popover);