public function findIn($haystack) : array
    {
        $matches = [];
        call_user_func_array(
            $this->_method,
            [
                sprintf("/%s/%s", $this->_expr, $this->_flags),
                $haystack,
                &$matches,
                $this->_pregMatchFlags ?: null,
            ]
        );

        if (!isset($matches[1]) && isset($matches[0]) && is_array($matches[0])) {
            return $matches[0];
        }

        return $matches;
    }