code: function (draggedElement, elementOffset, event) {
          return {
              element: draggedElement,
              posX: event.pageX - elementOffset.left,
              posY: event.pageY - elementOffset.top
          };
      }
docs: defaultDragImage returns the current item as dragged image
  @param {HTMLElement} draggedElement - the item that the user drags
  @param {object} elementOffset - an object with the offsets top, left, right & bottom
  @param {Event} event - the original drag event object
  @return {object} with element, posX and posY properties