Custom toolbar split button

<textarea id="custom-toolbar-split-button">
  <p><img style="display: block; margin-left: auto; margin-right: auto;" title="Tiny Logo" src="https://www.tiny.cloud/docs/images/logos/android-chrome-256x256.png" alt="TinyMCE Logo" width="128" height="128" /></p>
  <h2 style="text-align: center;">Welcome to the TinyMCE editor demo!</h2>
  <p>Select a menu item from the listbox above and it will insert contents into the editor at the caret position.</p>

  <h2>Got questions or need help?</h2>
  <ul>
    <li>Our <a href="https://www.tiny.cloud/docs/">documentation</a> is a great resource for learning how to configure TinyMCE.</li>
    <li>Have a specific question? Try the <a href="https://stackoverflow.com/questions/tagged/tinymce" target="_blank" rel="noopener"><code>tinymce</code> tag at Stack Overflow</a>.</li>
    <li>We also offer enterprise grade support as part of <a href="https://www.tiny.cloud/pricing">TinyMCE premium plans</a>.</li>
  </ul>

  <h2>Found a bug?</h2>
  <p>If you think you have found a bug please create an issue on the <a href="https://github.com/tinymce/tinymce/issues">GitHub repo</a> to report it to the developers.</p>

  <h2>Finally ...</h2>
  <p>Don't forget to check out our other product <a href="http://www.plupload.com" target="_blank">Plupload</a>, your ultimate upload solution featuring HTML5 upload support.</p>
  <p>Thanks for supporting TinyMCE! We hope it helps you and your users create great content.
    <br>All the best from the TinyMCE team.</p>
</textarea>

tinymce.init({
  selector: 'textarea#custom-toolbar-split-button',
  toolbar: 'myButton',
  menubar: false,
  setup: function (editor) {
    editor.ui.registry.addSplitButton('myButton', {
      text: 'My Button',
      icon: 'info',
      tooltip: 'This is an example split-button',
      onAction: function () {
        editor.insertContent('<p>You clicked the main button</p>');
      },
      onItemAction: function (api, value) {
        editor.insertContent(value);
      },
      fetch: function (callback) {
        var items = [
          {
            type: 'choiceitem',
            icon: 'notice',
            text: 'Menu item 1',
            value: '&nbsp;<em>You clicked menu item 1!</em>'
          },
          {
            type: 'choiceitem',
            icon: 'warning',
            text: 'Menu item 2',
            value: '&nbsp;<em>You clicked menu item 2!</em>'
          }
        ];
        callback(items);
      }
    });
  },
  content_style: 'body { font-family:Helvetica,Arial,sans-serif; font-size:14px }'
});