code: protected final boolean fireUnhandledKeyStroke(KeyStroke keyStroke) {
          boolean handled = false;
          for(Listener listener: listeners) {
              handled = listener.onUnhandledKeyStroke(this, keyStroke) || handled;
          }
          return handled;
      }
docs: This method should be called when there was user input that wasn't handled by the GUI. It will fire the
  {@code onUnhandledKeyStroke(..)} method on any registered listener.
  @param keyStroke The {@code KeyStroke} that wasn't handled by the GUI
  @return {@code true} if at least one of the listeners handled the key stroke, this will signal to the GUI that it
  needs to be redrawn again.