The interface provides {HEAD ~ access} to the data elements and the order keys in {TAIL ~ the dataset} in a type safe manner 
in
The interface provides { HEAD ~ access } to the data elements and the order keys in { TAIL ~ the dataset } in a type safe manner
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH