code: func CutIndexKeyNew(key kv.Key, length int) (values [][]byte, b []byte, err error) {
  	b = key[prefixLen+idLen:]
  	values = make([][]byte, 0, length)
  	for i := 0; i < length; i++ {
  		var val []byte
  		val, b, err = codec.CutOne(b)
  		if err != nil {
  			return nil, nil, errors.Trace(err)
  		}
  		values = append(values, val)
  	}
  	return
  }
docs: // CutIndexKeyNew cuts encoded index key into colIDs to bytes slices.
  // The returned value b is the remaining bytes of the key which would be empty if it is unique index or handle data
  // if it is non-unique index.