If the flag is true, {HEAD ~ the OptionalSort operation} changes {TAIL ~ the order keys} of elements in the dataset 
changes
If the flag is true , { HEAD ~ the OptionalSort operation } changes { TAIL ~ the order keys } of elements in the dataset
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH