Re: More convenient default rollback for users

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <address@hidden>
> Date: Tue, 29 Mar 2016 17:44:15 +0200
> 
> When we introduce behavioural changes in Emacs, we often include a way
> to get back to the old behaviour, and we document this in NEWS etc.
> 
> But wouldn't it be nice if we had this in a more convenient,
> cut-and-pastable format?
> 
> Imagine you're using Emacs 26 for the first time.  Suddenly you notice
> that when you hit the `hyper z' key, Emacs doesn't florbnoze as it used
> to, but forblizes instead!  You're furious!  So you hit the `C-h R' (for
> rollback) keystroke, and you get a buffer that looks like:
> 
> -------------
> ;; To roll back changes between Emacs 26 and Emacs 25.1:
> 
> ;; If you want the `hyper z' key still to florbnoze instead of
> ;; forblizing:
> (setq hyper-z-mode 'florbnoze)
> 
> ... more setqs here...
> 
> ;; To roll back changes between Emacs 25.1 and Emacs 24.3:
> 
> ...
> -------------

How do you do that with defcustoms?