code: private function checkUrl()
      {
          $legacyKernel = Eresus_CMS::getLegacyKernel();
          if ($this->getPage()->topic)
          {
              $acceptUrl = $legacyKernel->request['path'] .
                  ($this->getPage()->subpage !== 0 ? 'p' . $this->getPage()->subpage . '/' : '') .
                  ($this->getPage()->topic !== false ? $this->getPage()->topic . '/' : '');
              if ($acceptUrl != $legacyKernel->request['url'])
              {
                  $this->getPage()->httpError(404);
              }
          }
          else
          {
              $acceptUrl = $legacyKernel->request['path'] .
                  ($this->getPage()->subpage !== 0 ? 'p' . $this->getPage()->subpage . '/' : '');
              if ($acceptUrl != $legacyKernel->request['url'])
              {
                  $this->getPage()->httpError(404);
              }
          }
      }
docs: Проверяет URL на «существование»
  
  @since 3.01