Leafo\ScssPhp\Parser::stripOptionalFlag PHP Method

    protected function stripOptionalFlag(&$selectors)
    {
        $optional = false;
        $selector = end($selectors);
        $part = end($selector);
        if ($part === ['!optional']) {
            array_pop($selectors[count($selectors) - 1]);
            $optional = true;
        }
        return $optional;
    }