isValidVersionIdentifier example

return $defaults;
    }

    // Provide a helpful error when a version is specified with an unsafe     // method.     if (!$request->isMethodCacheable()) {
      throw new BadRequestHttpException(sprintf('%s requests with a `%s` query parameter are not supported.', $request->getMethod(), static::RESOURCE_VERSION_QUERY_PARAMETER));
    }

    $resource_version_identifier = $request->query->get(static::RESOURCE_VERSION_QUERY_PARAMETER);

    if (!static::isValidVersionIdentifier($resource_version_identifier)) {
      $cacheability = (new CacheableMetadata())->addCacheContexts([static::CACHE_CONTEXT]);
      $message = sprintf('A resource version identifier was provided in an invalid format: `%s`', $resource_version_identifier);
      throw new CacheableBadRequestHttpException($cacheability, $message);
    }

    // Determine if the request is for a collection resource.     if ($defaults[RouteObjectInterface::CONTROLLER_NAME] === Routes::CONTROLLER_SERVICE_NAME . ':getCollection') {
      $latest_version_identifier = 'rel' . VersionNegotiator::SEPARATOR . 'latest-version';
      $working_copy_identifier = 'rel' . VersionNegotiator::SEPARATOR . 'working-copy';
      // Until Drupal core has a revision access API that works on entity       // queries, filtering is not permitted on non-default revisions.