LD3 Core Class PHP

/* Warning: Undefined variable $_SERVER['DOCUMENT_ROOT'] in C:\xampp-8.1.6-0\projects\test.puzzlum.org.6.test\public\LD3\Linedancer\scripts\php\LD3 Framework\LD3 Classes\LD3 Core Class.php on line 222 */

                        if
                        (
                            preg_match_all
                            (
                                '/\{\$(?<key>[^{}]+)\}/xi',
                                $lines[$index],
                                $matches,
                                PREG_SET_ORDER
                            )
                        )
                        {
                            if(isset($_GET['track']))
                            {
                                print_r("Key match on line: {$index}\r\n");
                            }
                            foreach($matches as $match)
                            {
                                if(isset($match['key']))
                                {
                                        $key = $match['key'];
                                        $lines[$index] = str_replace($key,$$key,$lines[$index]); // line 222
                                    if(isset($_GET['track']))
                                    {
                                        print_r("{$key} = {$$key}");
                                    }
                                }
                            }
                        }