docs: def main(argv):
      """Validate a model's performance on a set of holdout data."""
      _, *validation_paths = argv
      if FLAGS.expand_validation_dirs:
          tf_records = []
          with utils.logged_timer("Building lists of holdout files"):
              for record_dir in validation_paths:
                  tf_records.extend(gfile.Glob(os.path.join(record_dir, '*.zz')))
      else:
          tf_records = validation_paths
  
      if not tf_records:
          raise RuntimeError("Did not find any holdout files for validating!")
      validate(*tf_records)