code: def validate_ipv6_addr(value)
        ipaddr = IPAddr.new(value)
        unless ipaddr.ipv6?
          raise ValidationError, "IP address '#{value}' is not IPv6"
        end
        ipaddr
      rescue ArgumentError => e
        raise ValidationError, "invalid IPv6 address '#{value}' - #{e.message}"
      end
docs: Validate that the given string _value_ describes a well-formed
   IPV6 network address using the standard "ipaddr" ruby module.