What is the AppContainer widget?

This widget is a placeholder for widgets that do stuff. Essentially, this widget is the full-page app chrome that defines a header, footer and center region (where your application goes). This widget also serves as an example of using pub/sub with widgets for all communication. When this widget wants to send a request to the server, it publishes its request on a topic. The control layer subscribes to this topic, performs the server call, and then publishes the response on a different topic. Widgets in this framework are not aware that a control layer exists.