Updates:
Status: WontFix
Comment #2 on issue 396 by alexandr...(a)gmail.com: Mondrian should provide
teh start and end nodes in the edge action
http://code.google.com/p/moose-technology/issues/detail?id=396
In Roassal, the block in on:do: receives an event, that contains the model.
Much cleaner than in Mondrian!