Called by the link internals to set an attribute on this node.
Source
Response setAttribute(String name, Object value, Responder responder,
Response response) {
if (!attributes.containsKey(name) || attributes[name] != value) {
attributes[name] = value;
updateList(name);
if (provider is SerializableNodeProvider) {
(provider as SerializableNodeProvider).persist();
}
}
return response..close();
}