Different formatting for digits resp. before and after decimal point

Hello,

When writing a decimal number, it is a common usage to typeset the digits after the decimal separator differently from the digits of the integral part:

• E.g., when indicating a price, it is very common, in many countries, to typeset the number of cents in superscript;
• Also, on French roadsigns (and possibly in other countries), the official norm requires the digits after the decimal comma to be typeset in a smaller font : see e. g. here.

At the time I used the (now unmaintained) package numprint (which siunitx takes some of its inspiration from), there was an internal command \nprt@printafter which could be hacked to get the desired effect. But now that I am using siunitx, I could not find such a feature in the current implementation...

Anyway, it would be nice that the siunitx would include the possibility (without any internal hacking by the user, I mean) to typeset post-decimal-point digits differently from the integer part (e.g. in a smaller font size, or as a superscript, or as text figures, or without thousand grouping, &c., &c.): for it is a common usage as explained above, and a quite convenient one IMHO!

Kind regards,
    /Soldyesis

Start by reviewing siunitx's number-formatting behavior and the issue's reference to numprint's internal command \nprt@printafter. Determine the intended scope for formatting digits after the decimal separator, including font size, superscript, text figures, and grouping. Done should provide a documented user-facing way to apply the selected formatting without internal hacking.