code: func (o *FilterOpt) Set(value string) error {
  	if value == "" {
  		return nil
  	}
  	if !strings.Contains(value, "=") {
  		return errors.New("bad format of filter (expected name=value)")
  	}
  	f := strings.SplitN(value, "=", 2)
  	name := strings.ToLower(strings.TrimSpace(f[0]))
  	value = strings.TrimSpace(f[1])
  
  	o.filter.Add(name, value)
  	return nil
  }
docs: // Set sets the value of the opt by parsing the command line value