Re: setnu-mode and Emacs 21.

[Richard Stallman]

      The next point Juanma is
    raising here, I think, is this: If we cannot use the display margin to
    display something on each line from the lisp level -- what use is 
    lisp access to the display margin.

We can use it for that.  But this method is best suited to displaying
material that is sparse and doesn't change too often.  Line numbers
are neither of those things: they are on every line, and a small
change in the file can change all of them.