On 2023-05-04 at 09:47, Lauri Vasama via Std-Proposals wrote:
> Floating an idea i've been toying around with for a while concerning a
> new syntax for attributes with observable effects on program behaviour.
>
> https://vasama.github.io/wg21/Dxxx1 <https://vasama.github.io/wg21/Dxxx1>
>
>

Don't see that an exclamation mark is a good choice for "required", as
it elsewhere means "not".

Like [[packed]] is optional, but [[!packed]] should be required packing.
To me it look more like unpacked.