JUndo is a declarative object-oriented language for addressing problems
such as multi-level undo that require objects to reside in multiple
simultaneous states.  The JUndo compiler produces Java source code that
can be used directly from existing Java projects.  I am going to be
giving a short presentation on the topic (as well as Verdantium, etc.)
on Sept. 26.  See http://www.ppjdg.org for more information about
location/etc.  For more general information on JUndo, see:
http://sourceforge.net/projects/jundo  For jundo-based examples see:
http://sourceforge.net/projects/verdantium