code: protected function calculateCacheKey()
      {
          $key = 'view_combination_' . strtolower(TL_MODE);
  
          // Authenticate the user - if this fails, we use an anonymous cache file.
          if ($this->authenticateUser()) {
              /** @noinspection PhpUndefinedFieldInspection */
              $key .= '_' . $this->getUser()->id;
          } else {
              $key .= '_anonymous';
          }
  
          return $key;
      }
docs: Try to load the combinations from cache.
  
  @return string|null