code: public static PathFilter newIndexDirFilter(Configuration conf) {
      return new PathFilters.CompositePathFilter(
        PathFilters.newExcludeFilesFilter(conf),
        PathFilters.EXCLUDE_HIDDEN_PATHS_FILTER,
        new PathFilter() {
          @Override
          public boolean accept(Path path) {
            return path.getName().startsWith("index-");
          }
        }
      );
    }
docs: Creates a path filter that accepts non-hidden directories that start with "index-"
  This is what the indexes created by this output format look like,
  so this is useful for finding them when traversing the file system