[NTG-context] Register with numeric values

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