If you ever want to add new items here, do not -- instead derive from popuplist or list query and override SetupWindowLayout(). (or if you can modify avkon, then add them here to make it easier for apps to use the new layout..) There's example at aknGMSstylegrid.cpp how to make new popup window without avkon modifications"
There is also a full example for T9, all thou the API it is completely non-public.
The doc you emntioned also mentions aknquerydialog.cpp, eikmenup.cpp and aknpopup.cpp, which looks also like a source codes for public API controls. So I think the page is atleast a bit misleading and as an general rule the SDK docs should not be read as absolute thruth, never really.