function getBBoxNest(element, baseWindow) {
    var left = 0, top = 0, bBox, frames;
    baseWindow = baseWindow || window;
    if (!(frames = getFrames(element, baseWindow))) { return null; }
    if (!frames.length) { // no frame
      return getBBox(element);
    }
    frames.forEach(function(frame, i) {
      var coordinates = getBBox(frame, i > 0); // relative to document when 1st one.
      left += coordinates.left;
      top += coordinates.top;
      coordinates = getContentOffset(frame);
      left += coordinates.left;
      top += coordinates.top;
    });
    bBox = getBBox(element, true);
    bBox.left += left;
    bBox.right += left;
    bBox.top += top;
    bBox.bottom += top;
    return bBox;
  }
Get an element's bounding-box that contains coordinates relative to document of specified window.
@param {Element} element - Target element.
@param {Window} [baseWindow] - Window that is base of coordinates.
@returns {(BBox|null)} A bounding-box or null when failed.