Creating a Rich UI application with multiple handlers

You can use multiple Rich UI handler parts to compose a single application. However, we do not mean to say that you embed one handler part in another. Instead, the handler part declares variables that are each based on another handler part. A variable based on an Rich UI handler part is called an embedded handler, as in the following example: 
embeddedHandler AnotherHandlerPart{};  // declared Rich UI handler 
                                          (based on part AnotherHandlerPart)

The embedding Rich UI handler can access the global widgets and public functions declared in an embedded Rich UI handler. In particular, the embedding handler can add widgets to its own initialUI and children arrays. Also, you can embed a handler that invokes services or otherwise handles business processing. A reasonable practice is to use one handler to present the UI and to use other handlers to oversee the backend, business processing.

You access widgets and functions with a dot syntax. In the following outline, the Handler part AnotherHandlerPart is assumed to have declared a button named itsButton, which is attached to the DOM tree only when that button is included in the initialUI array of the embedding handler:
handler SimpleHandler type RUIHandler { initialUI = [ embeddedHandler.itsButton ] }
   embeddedHandler AnotherHandlerPart{};
end

Similarly, you can add an embedded widget to a children array.

You can access a function or property in an embedded widget by extending the a dot syntax. For example, the following statement retrieves the displayed text of the embedded Button itsButton:
   myString STRING = embeddedHandler.itsButton.text;

The initialUI array of the embedded handler has no effect at run time. That array is used only when the embedded handler is the basis of a Rich UI application and is not embedded at all.