well... basicly let's say that we have a box or a crate in the middle of the screen... and view is top-down.
in the middle of the layout we only see its top (the sides have length 0)
if we scroll or drag/drop that box to the right side we would see its side (length would increase) as well... something like paralax or fake 3D.
see this example:
dl.dropbox.com/u/148996943/top3d.capx