show(msg, {timeout = 1500} = {}) {
    const node = typeof msg === 'string' ? new Text(msg) : msg;

    // Hacky heuristic: if we're currently showing a notification w/out a
    // timeout, and the new one includes a timeout, leave the existing one
    // alone.  We should rework this stack a bit to give more power to the
    // callers, but for now, this should be OK.
    if (this.container_.parentNode && this.timeout_ === null &&
        timeout !== null) {
      return;
    }

    // Remove all children first.
    this.container_.textContent = '';
    this.container_.appendChild(node);
    this.container_.style.opacity = '0.75';

    // Display on the page if it isn't already.
    if (!this.container_.parentNode) {
      this.parent_.appendChild(this.container_);
    }

    // Keep the notification centered.
    const size = this.container_.getBoundingClientRect();
    this.container_.style.top = `calc(50% - ${size.height / 2}px)`;
    this.container_.style.left = `calc(50% - ${size.width / 2}px)`;

    if (this.reader_) {
      this.reader_.assertiveAnnounce(this.container_.textContent);
    }

    // Handle automatic hiding of the UI.
    if (this.timeout_) {
      clearTimeout(this.timeout_);
      this.timeout_ = null;
    }
    if (timeout === null) {
      return;
    }
    this.timeout_ = setTimeout(() => {
      this.container_.style.opacity = '0';
      this.timeout_ = setTimeout(() => this.hide(), this.fadeout_);
    }, timeout);
  }
Show a notification for the specified duration.

The notification appears in inverse video, centered over the terminal.

@param {string|!Node} msg The message to display.
@param {{
    timeout: (?number|undefined),
}=} options
    timeout: How long (millisec) to wait before hiding the notification.
        Pass null to never autohide.