docs: public void getElementForDragAndDropFromContainer(
          final String clientId,
          final String containerId,
          boolean alwaysCopy,
          final I_CmsSimpleCallback<CmsContainerElementData> callback) {
  
          SingleElementAction action = new SingleElementAction(clientId, alwaysCopy, callback);
          action.setDndContainer(containerId);
          action.execute();
      }