code: private function logServerVals()
      {
          $logEnvInfo = $this->debug->getCfg('logEnvInfo');
          if (!$logEnvInfo['serverVals']) {
              return;
          }
          $logServerKeys = $this->debug->getCfg('logServerKeys');
          if (isset($_SERVER['REQUEST_METHOD']) && $_SERVER['REQUEST_METHOD'] !== 'GET') {
              $logServerKeys[] = 'REQUEST_METHOD';
          }
          if (isset($_SERVER['CONTENT_LENGTH'])) {
              $logServerKeys[] = 'CONTENT_LENGTH';
              $logServerKeys[] = 'CONTENT_TYPE';
          }
          if (!$logEnvInfo['headers']) {
              $logServerKeys[] = 'HTTP_HOST';
          }
          $logServerKeys = \array_unique($logServerKeys);
          if (!$logServerKeys) {
              return;
          }
          $vals = array();
          foreach ($logServerKeys as $k) {
              if (!\array_key_exists($k, $_SERVER)) {
                  $vals[$k] = $this->debug->abstracter->UNDEFINED;
              } elseif ($k == 'REQUEST_TIME') {
                  $vals[$k] = \date('Y-m-d H:i:s T', $_SERVER['REQUEST_TIME']);
              } else {
                  $vals[$k] = $_SERVER[$k];
              }
          }
          \ksort($vals, SORT_NATURAL);
          $this->debug->log('$_SERVER', $vals);
      }
docs: Log $_SERVER values specified by `logServerKeys` config option
  
  @return void