private function generateNegation($match)
    {
        $match = str_split($match);
        $chars = str_split($this->getChars());
        foreach ($match as $negVal) {
            if (($key = array_search($negVal, $chars)) !== false) {
                if ($negVal == '\\') {
                    continue;
                }
                unset($chars[$key]);
            }
        }

        return implode('', $chars);
    }