[m-rev.] for post-commit review: document requirement for non-abstract instances in interfaces

[Julien Fischer]

On Thu, 3 Feb 2022, Zoltan Somogyi wrote:

>
> 2022-02-03 13:45 GMT+11:00 "Julien Fischer" <jfischer at opturion.com>:
>>> I will reword what I added to take that into account, but section 10.4 does NOT
>>> mention this point (neither does it deny it), and does not give an example
>>> either.
>>
>> That's because type class constraints on instances have not been
>> discussed at all at that point.
>
> I already sent the diff making the changes you requested around 1:15pm.
> Do you have any further comments? Because once we agree on the error message,

No, the new error message looks fine.  (I've just committed a couple of
minor corrections to the reference manual change.)

Julien.