code: function getBorder(el) {
    var body = document.body;
    var workArea = findParent(el, function (v) {
      return hasClass(v, 'work-area');
    });
    var of = getOffset(workArea);
    return {
      left: of.x,
      right: of.x + workArea.offsetWidth,
      top: of.y + 50,
      bottom: body.offsetHeight < glb().innerHeight ? glb().innerHeight : body.offsetHeight
    };
  }
docs: get border