protected function validateProtocolVersion($protocolVersion) : void
	{
		if (! \is_string($protocolVersion))
		{
			throw new \InvalidArgumentException('HTTP protocol version must be a string');
		}
		else if (! \preg_match('/^\d(?:\.\d)?$/', $protocolVersion))
		{
			throw new \InvalidArgumentException(\sprintf('The given protocol version "%s" is not valid', $protocolVersion));
		}
	}