findNavPath(manifestNode) {
    // Find item with property "nav"
    // Should catch nav irregardless of order
    // var node = manifestNode.querySelector("item[properties$='nav'], item[properties^='nav '], item[properties*=' nav ']");
    var node = Object(core["qsp"])(manifestNode, "item", {
      "properties": "nav"
    });
    return node ? node.getAttribute("href") : false;
  }
Find TOC NAV
@private
@param {element} manifestNode
@return {string}