it requires further testing.

The implementation uses its own Engine and traverse since browser 
pages configured through ZCML are looked up by a bobo_traverse()
hack. However the standdard simpleTraverse() method of zope.tales.
expressions only performs the traversal using __getitem__(). So we
define our own traverser that also tries a traversal using 
restrictedTraverse().

The code is still ugly, needs some more cleanup and renaming.