code: public Object unmarshal(HierarchicalStreamReader reader,
  			UnmarshallingContext context) {
  		URI uri = URI.create(reader.getAttribute("uri"));
  		return XExtensionManager.instance().getByUri(uri);
  	}
docs: /* (non-Javadoc)
  @see com.thoughtworks.xstream.converters.Converter#unmarshal(com.thoughtworks.xstream.io.HierarchicalStreamReader, com.thoughtworks.xstream.converters.UnmarshallingContext)