Re: reverting non-file buffers in earlier Emacs versions.

[Richard Stallman]

Mentioning this in emacs-xtra.texi could be useful if it is done
in a slightly different way:

    + This chapter describes the behavior in Emacs versions 21.4 or later.

It is redundant to say so here.  Everything in this manual that comes
with Emacs 21.4 will describe something about Emacs version 21.4.

    + In earlier versions, auto-reverting of non-file buffers, while
    + possible, could cause several problems such as excessive reverts,
    + excessive noisiness, inappropriate point movement and the like.

It is useful to say that.  "In earlier versions" could be replaced
with "In Emacs versions before 21.4".

The change in autorevert.el is unnecessary.  Anyone who sees that doc
string will see it in Emacs 21.4 only.