EDIT

  /**

   * Provides the content of foot notes

   *

   * @param string $footnoteListKey

   *

   * @return array

   *   The content of foot notes or an empty array if the $footnoteListKey is

   *   blocked

   */

  public static function footnoteListContents($footnoteListKey) {

    if(self::isBlockedFootnoteListKey($footnoteListKey)){

      // the footnote key is blocked, don't render it!

      return [];

    }

    $content_list = [];

    if (array_key_exists($footnoteListKey, self::$fnstore)) {

      foreach (self::$fnstore[$footnoteListKey] as $fn) {

        $content_list[] = $fn->getContent();

      }

    }

    return $content_list;

  }