code: public void marshal(Object obj, HierarchicalStreamWriter writer,
  			MarshallingContext context) {
  		XExtension extension = (XExtension)obj;
  		writer.addAttribute("uri", extension.getUri().toString());
  	}
docs: /* (non-Javadoc)
  @see com.thoughtworks.xstream.converters.Converter#marshal(java.lang.Object, com.thoughtworks.xstream.io.HierarchicalStreamWriter, com.thoughtworks.xstream.converters.MarshallingContext)