Re: What lookup-key returns for an undefined key

[Luc Teirlinck]

Eli Zaretskii wrote"
   
   In Emacs 21.3, lookup-key returns `undefined' for an undefined key; in
   the current CVS it returns nil.

   If this change is intentional, I think we should reflect that in NEWS.

   Two bundled Lisp packages are affected by this: woman.el and
   gnus-util.el.  I've fixed the former, but not the latter.

There are three types of key that are commonly referred to as
"undefined":  keys that are not bound, keys bound to the symbol nil and
keys bound to the command `undefined'.  If nothing else tries to
define the key, the end result is the same, in as far as the user is
concerned.  If something else tries to define the key, there are
subtle differences.  `lookup-key' returns nil for the first two types
and `undefined' for the latter.

`dired-mode-map' used by woman.el has been changed from 21.3 to unbind
several keys that were formerly bound to the command `undefined'.  I
believe that your change to woman.el is correct.  However that code
was _already_ broken in 21.3.  Probably, gnus-util.el needs a similar
change.

Sincerely,

Luc.