private function toggle():void {
     try {
     switch (systemManager.stage.displayState) {
       case StageDisplayState.FULL_SCREEN:
            systemManager.stage.displayState = StageDisplayState.NORMAL;
            break;
       default: systemManager.stage.displayState = StageDisplayState.FULL_SCREEN;
       break;
       }
     } catch (err:SecurityError) {
                          // ignore
       }
    }