On 2017-07-02 12:54, Noam Postavsky wrote:
> On Sun, Jul 2, 2017 at 12:32 PM, Clément Pit-Claudel
> <cpitclaudel@gmail.com> wrote:
>>> Why would we need a new function since %n$ would be an error for the old format anyway?
>>
>> This in itself is a good reason to have a new function.  A new function lets you migrate existing code, including plugins, to the new syntax, and load the polyfill in older Emacsen.  A new syntax that causes errors in old Emacsen isn't usable by anyone outside of Emacs core, for fear of compatibility problems.
>
> We can still give a new name I suppose.

I think it would be nice, if we also write a polyfill. If we don't intend to write one, then there's probably no point.