[Tim]
> Note that transforming
>
>     {EXPR!d:FMT}
>
> into
>
>     EXPR={repr(EXPR):FMT}
>
> is actually slightly more involved than transforming it into
>
>     EXPR={EXPR:FMT}
>
> so I don't buy the argument that the original idea is simpler.  More
> magical and less useful, yes ;-)

[Eric V. Smith]
Actually, my proposal is to apply FMT to the entire result of 
EXPR={repr(EXPR)}, not just the repr(EXPR) part. I'm not sure either is
particularly useful.

So the actual transformation is from

    {EXPR!d:FMT}

to

    {"EXPR=" + repr(EXPR):FMT}

I expect I'll barely use "!d" at all if the format doesn't apply to the result of EXPR, so I have no non-contrived ;-) opinion about that.

BTW, I checked, and I've never used !r, !s, or !a.  So the idea that the format could apply to a string - when EXPR itself doesn't evaluate to a string - is simply foreign to me.  I suppose it's natural to people who do use ![rsa] all the time - if such people exist ;-)