le title bar area.
            <ol>
              <li>If there is only one overlay region in |ovls|, set |tba| as a
              {{DOMRect}} that encompasses the area from the edge of the frame
              to the innermost edge of the |ovls|.
              </li>
              <li>If there is more than one overlay region in |ovls|, set |tba|
              to a {{DOMRect}} that encompasses the area between the
              intersection of the regions in |ovls| and the [=document=]'s
              <a href=