[NTG-context] Register with numeric values

[luigi scarso]

I'm using register with numeric values, eg
\defineregister[MyReg][MyRegs]
\starttext
123\MyReg[123]
345\MyReg[345]
aaa\MyReg[aaa]
\page
\placeMyReg
\stoptext

but there aren't head as for entry 'aaa'.
I'm looking into core-reg, but I've not ideas.

luigi