> I'm not really interested in the mode itself, but rather with what it
 > does to display engine.  So I will be looking at this at an entirely
 > different level than you seem to think.  At that level, it is not
 > important for me to understand what the Lisp code does, just what
 > display feature it uses and what that does to redisplay.

OK.  I attach a zipped version of the code.  The function that is most
bidi-incompatible is `sidebar-match-list' and its use of invisibility
and overlays which is probably highly indigestible.

martin