code: func (c *Certificates) String() string {
  	if len(*c) == 0 {
  		return ""
  	}
  	var result []string
  	for _, certificate := range *c {
  		result = append(result, certificate.CertFile.String()+","+certificate.KeyFile.String())
  	}
  	return strings.Join(result, ";")
  }
docs: // String is the method to format the flag's value, part of the flag.Value interface.
  // The String method's output will be used in diagnostics.