docs: private static void addButton(JFrame frame, String s) {
          AnnotatedString as = new AnnotatedString(s);
          JButton button = new JButton(as.toString());
          button.setMnemonic(as.getMnemonic());
          button.setDisplayedMnemonicIndex(as.getMnemonicIndex());
          frame.getContentPane().add(button);
  
          System.out.println("\"" + s + "\" \"" + as + "\" '" + as.getMnemonic() + "' " + as.getMnemonicIndex());
      }