Fri Apr 6 01:16:06 CEST 2012

Equations for box layout

Turns out there is a specific kind of equation that doesn't seem to be
easier to implement than with a dedicated algorithm that reflects its
recursive structure directly:

   - sum child box sizes into one box, propagate upward
   - receive 1 location and scale info and propagate downward

The algorithm is a very elegant approach using continuations to chain
everthing together.  More later!