/**
   * Create a new IFrame widget.
   *
   * #### Notes
   * Once layout restoration is fully supported, the hidden state of the IFrame
   * widget will be handled by the layout restorer and not by the message hook
   * handler in this function.
   */
  function newIFrame(id: string): IFrame {
    let iframe = new IFrame();
    iframe.addClass(HELP_CLASS);
    iframe.title.label = 'Help';
    iframe.id = id;

    // If the help widget is being hidden, remove its state.
    installMessageHook(iframe, (iframe: IFrame, msg: Message) => {
      if (msg === WidgetMessage.BeforeHide) {
        state.remove(key);
      }
      return true;
    });

    return iframe;
  }

  /**
   * Create a new IFrame widget.
   */
  function newIFrame(url: string): IFrame {
    let iframe = new IFrame();
    iframe.addClass(HELP_CLASS);
    iframe.title.label = category;
    iframe.id = `${namespace}`;
    iframe.url = url;
    // Add the iframe to the instance tracker.
    tracker.add(iframe, { area: 'right' });

    // If the help widget visibility changes, update the tracker.
    installMessageHook(iframe, (iframe: IFrame, msg: Message) => {
      switch (msg) {
        case WidgetMessage.AfterShow:
        case WidgetMessage.BeforeHide:
          // Wait until hide has completed.
          requestAnimationFrame(() => { tracker.save(iframe); });
          break;
        default:
          break;
      }
      return true;
    });
    return iframe;
  }