[NTG-context] how to do something like ^1/_2 with frac?

[Hubertus]

Hi all again,
I try to do something like 1/2 with an upper 1 and a lower 2. The code below
still doesn't quite work. 

\def\nfrac#1#2{\leavevmode\kern.1em%
  \raise.5ex\hbox{\scriptsize #1}%
  \kern-.1em/\kern-.15em%
  \lower.25ex\hbox{\scriptsize #2}}

Help would be very much appreciated!

Hubertus

P.S. Is there a good pdf around to get some insight's of this tex-magic?