%b decimalless scientific notation with exponent a power of two,
in the manner of strconv.FormatFloat with the 'b' format,
e.g. -123456p-78
- %e scientific notation, e.g. -1234.456e+78
- %E scientific notation, e.g. -1234.456E+78
+ %e scientific notation, e.g. -1.234456e+78
+ %E scientific notation, e.g. -1.234456E+78
%f decimal point but no exponent, e.g. 123.456
%F synonym for %f
%g %e for large exponents, %f otherwise