First App extension to enable the nested Y.Apps functionality: AppNestable. This provides an attribute and function for ensuring Pjax URLs have the correct path (as on non-pushState browsers the original 'root' may have been misled by the top level application into being the path after the #).
Second App extension to enable the nested Y.Apps functionality: AppNestanator. This provides a function for nesting another Y.App inside the current Y.App and another function for uprooting it.
Build files from the last few commits.