code: @Override
     protected void entering(NodeData node, int level) throws RepositoryException
     {
        super.entering(node, level);
        try
        {
           writer.writeAttribute(Constants.NS_EXO_PREFIX, Constants.NS_EXO_URI, Constants.EXO_ID, node.getIdentifier());
  
        }
        catch (XMLStreamException e)
        {
           throw new RepositoryException(e);
        }
     }
docs: /*
  (non-Javadoc)
  @see
  org.exoplatform.services.jcr.impl.xml.exporting.SystemViewStreamExporter#entering(org.exoplatform
  .services.jcr.datamodel.NodeData, int)