code: func (h *Handle) validateOrdinal(ordinal uint64) error {
  	h.Lock()
  	defer h.Unlock()
  	if ordinal >= h.bits {
  		return errors.New("bit does not belong to the sequence")
  	}
  	return nil
  }
docs: // checks is needed because to cover the case where the number of bits is not a multiple of blockLen