public function getModifiers()
    {
        $mods = $this->modifiers;
        if ($this->getIgnoreCase()) {
            $mods .= 'i';
        } elseif ($this->getIgnoreCase() === false) {
            $mods = str_replace('i', '', $mods);
        }
        if ($this->getMultiline()) {
            $mods .= 's';
        } elseif ($this->getMultiline() === false) {
            $mods = str_replace('s', '', $mods);
        }
        // filter out duplicates
        $mods = preg_split('//', $mods, -1, PREG_SPLIT_NO_EMPTY);
        $mods = implode('', array_unique($mods));

        return $mods;
    }