protected function isSpecialLine($line)
    {
        if (strlen($line) < 3) {
            return false;
        }

        $letter = $line[0];

        $environment = $this->environment;
        if (!in_array($letter, $environment::$letters)) {
            return false;
        }

        for ($i=1; $i<strlen($line); $i++) {
            if ($line[$i] != $letter) {
                return false;
            }
        }

        return $letter;
    }