Comment #9 on issue 888 by tu...@tudorgirba.com: MondrianViewBuilder should support a better zOrder http://code.google.com/p/moose-technology/issues/detail?id=888
Indeed, all elements should be rendered independently of their nesting level :).
That is why it is important to have the zIndex in the element, and ideally, we should also store the order by level in the ZOrdering.