code: private function clearAlerts($flags)
      {
          $clearAlerts = $flags & Debug::CLEAR_ALERTS;
          if (!$clearAlerts) {
              return null;
          }
          if ($this->channelName) {
              foreach ($this->data['alerts'] as $i => $entry) {
                  $channel = isset($entry[2]['channel']) ? $entry[2]['channel'] : null;
                  if ($this->channelTest($channel)) {
                      unset($this->data['alerts'][$i]);
                  }
              }
              $this->data['alerts'] = \array_values($this->data['alerts']);
          } else {
              $this->data['alerts'] = array();
          }
          return 'alerts';
      }
docs: Clear alerts
  
  @param integer $flags flags passed to clear()
  
  @return string|null