code: func ApplicationWindowNew(app *Application) (*ApplicationWindow, error) {
  	c := C.gtk_application_window_new(app.native())
  	if c == nil {
  		return nil, nilPtrErr
  	}
  	return wrapApplicationWindow(glib.Take(unsafe.Pointer(c))), nil
  }
docs: // ApplicationWindowNew is a wrapper around gtk_application_window_new().