public static function isValidRfc(string $rfc): bool
    {
        return in_array($rfc, [self::RFC_2616, self::RFC_7230]);
    }
public static function isValidRfc(string $rfc): bool
    {
        return in_array($rfc, [self::RFC_2616, self::RFC_7230]);
    }
public static function isValidRfc ( string $ rfc ) : bool { return in_array ( $ rfc , [ self :: RFC_2616 , self :: RFC_7230 ] ) ; }
checks if given RFC is a valid and known RFC

@param   string  $rfc
@return  bool
checks if given RFC is a valid and known RFC