I feel like this is still an unsolved notational problem. Let's say I want to give you the elevation of Mt Everest in feet to 3 sig figs. I could say 29,000 ft, but that'd be misread as 2 sig figs. So I have to say something like 29010^2 , or 2.9010^4 , to convey the correct information. Or just 2.90e4. Maybe there's nothing better?
Famously, the original surveyor of Mt Everest calculated 29,000 exactly but lied and added 2 feet to make it 29,002 so that people would understand he meant 5 sig figs, not just 2. That's one way of solving the problem ...
It bothers me that this overloads the notation for repeating fractions. I guess there wouldn't be a use case requiring both in a single number, but you can imagine multiple numbers on the same page using this formatting for different purposes and it being confusing.
And it's fine for writing out by hand or in TeX (I assume), but good luck using it in any other context as we see here! Ideally a notation would be keyboard-friendly, at least for something with as wide an applicability as this anyway.
Famously, the original surveyor of Mt Everest calculated 29,000 exactly but lied and added 2 feet to make it 29,002 so that people would understand he meant 5 sig figs, not just 2. That's one way of solving the problem ...