private function decodeSplitPart($entity)
    {
        if (preg_match("/^=\?([A-Za-z\-_0-9]+)\*?([A-Za-z\-_0-9]+)?\?([QBqb])\?([^\?]+)\?=$/", $entity, $matches)) {
            return $this->decodeMatchedEntity($matches);
        }
        $decoded = $this->convertEncoding($entity);
        $this->addToLanguage($decoded);
        return $decoded;
    }