class AppDeleatate: NSObject, NSApplicationDelegate {
  fileprivate var optionalMenuItems = [NSMenuItem]()
  //...
  
  func applicationDidFinishLaunching(_ aNotification: Notification) {
        //...
        let specialItem = NSMenuItem(title: MenuBarItemLabelText.specialItem, action: #selector(doNeatAction), keyEquivalent: "")
        specialItem.isHidden = true
            
        optionalMenuItems.append(specialItem)
        //...
  }
}

//MARK: NSMenuDelegate + Option key shows additional menu items
extension AppDelegate: NSMenuDelegate {
    
    func menuWillOpen(_ menu: NSMenu) {
        if menuObserver == nil {
            menuObserver = CFRunLoopObserverCreateWithHandler(nil, CFRunLoopActivity.beforeWaiting.rawValue, true, 0, { (observer, activity) in
                self.menuRecievedEvents()
            })
            
            CFRunLoopAddObserver(CFRunLoopGetCurrent(), menuObserver, CFRunLoopMode.commonModes)
        }
    }
    
    func menuDidClose(_ menu: NSMenu) {
        guard menuObserver != nil else {
            return
        }
        CFRunLoopObserverInvalidate(menuObserver)
        menuObserver = nil
    }
    
    /// Will update the active menu. Used to update for events such as `OPTION` key presses.
    fileprivate func menuRecievedEvents() {
        // Get global modifier key flags
        let event = CGEvent(source: nil)
        let flags: CGEventFlags = event!.flags
        let optionKeyIsPressed = CGEventFlags(rawValue: flags.rawValue & CGEventFlags.maskAlternate.rawValue) == CGEventFlags.maskAlternate
        
        for item in optionalMenuItems {
            item.isHidden = !optionKeyIsPressed
        }
    }
}