// backup original libxmljs nextSibling() to newly named method
libxmljs.Element.prototype.nextSiblingOld = libxmljs.Element.prototype.nextSibling;

// new dom method, use a getter because this is invoked as an attribute
Object.defineProperties(libxmljs.Element.prototype, {
  nextSibling: {
    get: function() {
      return this.nextSiblingOld();
    }
  }
};