public function getModifiedKeys(array $diff) {
    $diff_keys = [];
    if (!empty($diff)) {
      foreach ($diff as $first_parent => $value) {
        // Collect all multidimensional parent keys + path to changed child key.
        if (is_array($value) && !empty($value) && count($value) == 1) {
          $diff_keys[] = $first_parent . '.' . $this->getChildKey($value);
        }
        else {
          $diff_keys[] = $first_parent;
        }
      }
    }

    return $diff_keys;
  }