code: function findDragElement(sortableElement, element) {
          var options = addData(sortableElement, 'opts');
          var items = _filter(sortableElement.children, options.items);
          var itemlist = items.filter(function (ele) {
              return ele.contains(element);
          });
          return itemlist.length > 0 ? itemlist[0] : element;
      }
docs: Dragging event is on the sortable element. finds the top child that
  contains the element.
  @param {HTMLElement} sortableElement a single sortable
  @param {HTMLElement} element is that being dragged