Error: `std.uni.isUpper` conflicts with `std.ascii.isUpper`

[aberba]

On Wednesday, 15 July 2020 at 07:01:34 UTC, WebFreak001 wrote:
> On Tuesday, 14 July 2020 at 20:37:53 UTC, Marcone wrote:
>> [...]
>
> Additionally to the other answers telling you how to fix it, 
> it's important to know why it happens in the first place:
>
> [...]

Without reading this very explanation, how would one know whilst 
reading docs?