code: private function getExtensions()
      {
          if (null === $this->sorted) {
              krsort($this->extensions);
              $this->sorted = !empty($this->extensions) ? call_user_func_array('array_merge', $this->extensions) : array();
          }
  
          return $this->sorted;
      }
docs: Sorts the internal list of extensions by priority.
  
  @return ExtensionInterface[]