A PanelStack is an combination of a ViewStack and Panel.
It extends ViewStack, and adds the panel features to it (NOTE you can’t treat the children as if they are in a Box, they are treated as if they are in a ViewStack).
Although you could put one of these together pretty easily by add a ViewStack as the only child to a Panel and making its width and height 100%, we recently required this functionality and this was a much cleaner approach for what we required, instead of overriding all the display list methods. Because it’s a ViewStack you can also use the Efflex viewStackEffects in there as you can see in the example.
The source for the example is available on right-click, but the source for the PanelStack itself is in our Google Code Library.