code: 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();
      }
docs: Requests the data for a container element specified by the client id for drag and drop from a container. The data will be provided to the given call-back function.<p>
  
  @param clientId the element id
  @param containerId the id of the container from which the element is being dragged
  @param alwaysCopy <code>true</code> in case reading data for a clipboard element used as a copy group
  @param callback the call-back to execute with the requested data