\starttext

\placeregister[index] \page

\setregisterentry[index][entries=entry1,keys=key1] page 2 \page

\setregisterentry[index][entries:1=entry21,entries:2=entry22] page 3 \page

\setregisterentry[index][entries:1=entry31,entries:2=entry32,keys:1=key31,keys:2=key32] page 4 \page

\stoptext

