xstream.processAnnotations(XStreamPacketExtension.class);
xstream.processAnnotations(classes);
xstream.alias(elementName, XStreamPacketExtension.class);
ProviderManager providerManager = ProviderManager.getInstance();
providerManager.addExtensionProvider(getElementName(), getNamespace(),
this);
providerManager.addIQProvider(getElementName(), getNamespace(), this);
// TODO Validate that elementName is a valid XML identifier
}