public function getRelativePath()
    {
        $current = realpath('./');

        if ($current !== false && strpos(self::$path.'/', $current.'/') === 0) {
            return rtrim('./' . substr(self::$path, strlen($current) + 1), '\\/');
        }

        throw new \InvalidArgumentException(
            'Unable to resolve relative path to Textpattern installation location '.
            'from the current working directory.'
        );
    }