code: public static void initializeForSorting(final SyndFeed feed) throws FeedException {
          // TODO: the null parameter below will break delegating parsers and generators
          // final ModuleGenerators g = new ModuleGenerators(feed.getFeedType() +
          // ITEM_MODULE_GENERATORS_POSFIX_KEY, null);
          final SyndFeedOutput output = new SyndFeedOutput();
          final Document document = output.outputJDom(feed);
          final SyndFeed copy = new SyndFeedInput().build(document);
          feed.copyFrom(copy);
      }
docs: This method will take a SyndFeed object with a SimpleListExtension on it and populate the
  entries with current SleEntry values for sorting and grouping. <b>NB</b>: This basically does
  this by re-generating the XML for all the entries then re-parsing them into the SLE data
  structures. It is a very heavy operation and should not be called frequently!