code: func createTxidRangeEndKey(txid string) []byte {
  	var endKey []byte
  	endKey = append(endKey, prwsetPrefix)
  	endKey = append(endKey, compositeKeySep)
  	endKey = append(endKey, []byte(txid)...)
  	// As txid is a fixed length string (i.e., 128 bits long UUID), 0xff can be used as a stopper.
  	// Otherwise a super-string of a given txid would also fall under the end key of range query.
  	endKey = append(endKey, byte(0xff))
  	return endKey
  }
docs: // createTxidRangeEndKey returns a endKey to do a range query on transient store using txid