public function exportTranslatable(TranslatableInterface $translatable, $targetLang) {
    $this->openMemory();
    $this->setIndent(TRUE);
    $this->setIndentString(' ');

    $this->startElement('xlf:group');
    $this->writeAttribute('id', $translatable->getIdentifier());
    $this->writeAttribute('restype', 'x-eggs-n-cereal-translatable');

    // Retrieve and flatten translatable data.
    $translatableData = $translatable->getData();
    $flattenedData = Data::flattenData($translatableData);

    // @todo: Write in nested groups instead of flattening it.
    $data = array_filter($flattenedData, array('EggsCereal\Utils\Data', 'filterData'));
    foreach ($data as $key => $element) {
      $this->addTransUnit($key, $element, $targetLang);
    }
    $this->endElement();
    return $this->outputMemory();
  }