code: func parseFlowSpecBitmaskOperand(submatch []string) (operand uint8, err error) {
  	if submatch[1] == "&" {
  		operand = BITMASK_FLAG_OP_AND
  	}
  	value, ok := BitmaskFlagOpValueMap[submatch[2]]
  	if !ok {
  		return 0, fmt.Errorf("invalid bitmask operand: %s%s", submatch[1], submatch[2])
  	}
  	operand |= uint8(value)
  	return operand, nil
  }
docs: // Parses the FlowSpec bitmask operand using the given submatch which should be
  // the return value of func (*Regexp) FindStringSubmatch.