A compliant implementation has no unimplemented features?

And a non-compliant implementation can warn for missing features in a hardcoded way.

Why should the standard library use it and why should it be in the standard?
 

-----Ursprüngliche Nachricht-----
Von: Hans Åberg via Std-Proposals <std-proposals@lists.isocpp.org>
>
> The most common use will not the in the Standard Library. Please design it
> with the most common use-case in mind.

The intended design is for use in the standard library.