Re: defcustom :version

[Richard Stallman]

    3. Refactor customize-changed to accept two new optional arguments which is
       the prefix of the package and the version symbol to use
       ('custom-version by default).

I don't like that idea, because I don't want to expose version numbers
of parts of Emacs to the user.

What could be acceptable is to have :package-version for use in
defcustom, and provide a table to translate that into Emacs versions,
so that customize-changed can deduce from :package-version which options
have changed since the previous Emacs release.