code: func IsIPv6(addr string) (bool, error) {
  	ip := net.ParseIP(addr)
  	if ip == nil {
  		return false, fmt.Errorf("invalid IP address: %q", addr)
  	}
  	return ip.To4() == nil, nil
  }
docs: // IsIPv6 returns true if provided IP address is IPv6, false otherwise