code: protected void addBundle (HashIntMap<TileSet> idmap, HashMap<String, Integer> namemap,
          ResourceBundle bundle)
      {
          try {
              TileSetBundle tsb = BundleUtil.extractBundle(bundle);
              // initialize it and add it to the list
              tsb.init(bundle);
              addBundle(idmap, namemap, tsb);
  
          } catch (Exception e) {
              log.warning("Unable to load tileset bundle '" + BundleUtil.METADATA_PATH +
                          "' from resource bundle [rbundle=" + bundle + "].", e);
          }
      }
docs: Extracts the tileset bundle from the supplied resource bundle
  and registers it.