code: func ValidateLogOpt(cfg map[string]string) error {
  	for key := range cfg {
  		switch key {
  		case "env":
  		case "env-regex":
  		case "labels":
  		case "labels-regex":
  		case "syslog-address":
  		case "syslog-facility":
  		case "syslog-tls-ca-cert":
  		case "syslog-tls-cert":
  		case "syslog-tls-key":
  		case "syslog-tls-skip-verify":
  		case "tag":
  		case "syslog-format":
  		default:
  			return fmt.Errorf("unknown log opt '%s' for syslog log driver", key)
  		}
  	}
  	if _, _, err := parseAddress(cfg["syslog-address"]); err != nil {
  		return err
  	}
  	if _, err := parseFacility(cfg["syslog-facility"]); err != nil {
  		return err
  	}
  	if _, _, err := parseLogFormat(cfg["syslog-format"], ""); err != nil {
  		return err
  	}
  	return nil
  }
docs: // ValidateLogOpt looks for syslog specific log options
  // syslog-address, syslog-facility.