I'm trying to use a StackContainer to create three different "screens" of my webapp, with any one viewable at a time.

I'm creating the "shell" of the StackContainer and three ContentPanes (inside the StackContainer) in markup, then filling out the real content of the ContentPanes later by assigning stuff to each of the ContentPanes' innerHTML. The size of the real content won't be known until some data is loaded (via an xhrGet()), but will certainly be larger than the "shell".