parseNcx(tocXml) {
    var navPoints = Object(core["qsa"])(tocXml, "navPoint");
    var length = navPoints.length;
    var i;
    var toc = {};
    var list = [];
    var item, parent;
    if (!navPoints || length === 0) return list;

    for (i = 0; i < length; ++i) {
      item = this.ncxItem(navPoints[i]);
      toc[item.id] = item;

      if (!item.parent) {
        list.push(item);
      } else {
        parent = toc[item.parent];
        parent.subitems.push(item);
      }
    }

    return list;
  }
Parse from a Epub > 3.0 NC
@private
@param  {document} navHtml
@return {array} navigation list