From: Erik Naggum <naggum.no at erik>

   |    well.  `undo-limit' (20000) and `undo-strong-limit' (30000) are the upper
   |    limits to how much undo information is kept, in bytes.
   
   as their documentation say, these limits apply when garbage collection
   happens.

Actually, the connection to gc is mentioned only for gs-strong-limit
(in 19.34).  A warning for anyone playing around with these two
variables, I noticed they are named differently in xemacs.

   no, undo is great for user input.  process output, however, should not be
   put on the undo list.

I agree with this design goal, as it makes exquisite sense and would
even allow intuitive use of undo while asynchronously entering text
while the previous interaction is still producting output.  But (as
you apparently admit) until the undo menchanisms support these things,
we have to make do with what we have.