code: func ValidateHost(val string) (string, error) {
  	host := strings.TrimSpace(val)
  	// The empty string means default and is not handled by parseDaemonHost
  	if host != "" {
  		_, err := parseDaemonHost(host)
  		if err != nil {
  			return val, err
  		}
  	}
  	// Note: unlike most flag validators, we don't return the mutated value here
  	//       we need to know what the user entered later (using ParseHost) to adjust for TLS
  	return val, nil
  }
docs: // ValidateHost validates that the specified string is a valid host and returns it.