>This sounds interesting, but also rather similar to what the `limit_denominator` method can get you. 

`Fractions("0.17").limit_denominator()` and `Fractions("0.17").limit_denominator(n)`
for n > 28 do not give 1/6.  So, I'd have to guess at n until I get 1/6.  Instead, I'd like to have the digits actually presented "0.17" determine the interval [0.165, 0.175) which then determines the fraction.

In particular, "0.170" would give a different answer ... a fraction within [0.1695, 0.1705).