Re: expand-file-name leaves "/../" in expansions at times

[Richard Stallman]

    I don't know anything about the Emacs code, but CMU CS had a networked
    filesystem (the mach/spice project vaxes) which had the concept of a
    super-root above /, accessed via "/..".  E.g. to access file "/x/y" on
    machine "blargh", you'd use "/../blargh/x/y" (IIRC, "/.." was a real
    directory so you could do "cd /..", "ls /.." to see all machines, etc)..

I think this is the Andrew file system.  Indeed, I think that is the
reason why Emacs doesn't convert `/..' to `/',

I don't know whether AFS is still used.  If not, we would like to
remove the support for it, by and by.  But there is certainly no
reason to remove it just now.

It would be good to add a sentence in the Emacs Lisp Reference Manual
to explain this.  Would someone please do that?