code: public void setDndArea(Object dndArea) {
          if(dndArea instanceof UIObject) {
              dndArea = ((UIObject) dndArea).getElement();
          }
          if(dnd != null) {
              dnd.draggable(JsDragOptions.create(new Restriction(dndArea, true, 0, 0, 1.2, 1)));
          }
      }
docs: Set the area for the drag and drop, can be an {@link Element}
  or a {@link String} selector.