No HTML has to be used and augmented to define the interface. The qooxdoo user does not even have to know CSS to style the interface. Clean and easy-to-configure themes for appearance, colors or icons allow for a full-fledged styling that even supports runtime switching.
While being a client-side and server-agnostic solution, the qooxdoo project does include complete implementations of RPC servers (currently Java and PHP) to demonstrate some of its advanced client-server communcation. An abstract transport layer supports queues, timeouts and implementations via XMLHttpRequest, Iframes and Scripts. Like the rest of qooxdoo it fully supports event-based programming which greatly simplifies asynchronous communication.