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Check out AjaxExample's Application class to see how this was registered.
JSON "Components" act like web-service end points, but provide statefulness similar to WOComponents in the regular WO framework. You can have components that are shared for the session or ones that are more transient (maybe it only exists for use on a single page). You can click the buttons below to see a stateful counter changing as a session global component as well as an instance component.