 for a window |win|, run these steps:
        </p>
        <ol>
          <li>If |win|'s [=overlay=] has had its width or height changed (e.g.
          as a result of the user resizing the browser window, or changing the
          page zoom factor, or other UI appearing or disappearing on the
          [=overlay=]), since the last time these steps were run, [=fire an
          event=] named `ongeometrychange` at the {{Window/window}} object and
          [=update the overlay area information=].
          <