title: Swift 5, NSTextField, controlTextDidChange gives compiler error "Method does not override any method from its superclass"
body: <p>I need to verify the characters in a <code>NSTextField</code> as they are being input. </p>
  
  <p>I've tried every solution proposed by google and I'm now tearing my hair out because <code>NSTextField</code> input verification is a standard thing to do, which means that I'm failing to understand something basic. </p>
  
  <pre><code>class MyWinController: NSWindowController, NSTextFieldDelegate {
  
      @IBOutlet var textField: NSTextField!
  
      override func windowDidLoad() {
          super.windowDidLoad()
      }
  
      @IBAction func textField(_ sender: Any) {
          print("MyWinController textField")
      }
  
      override func controlTextDidChange(notification: NSNotification) {
          print("APNewAPStaticWindowController controlTextDidChange")
      }
  }
  </code></pre>
  
  <p>The <code>textField</code> function works but when I include the <code>controlTextDidChange</code> function I get the compiler error: <code>Method does not override any method from its superclass</code>.</p>
  
  <p>Help would be greatly appreciated. Thanks.</p>