code: public function onError(Event $error)
      {
          if ($this->debug->getCfg('collect')) {
              /*
                  temporarily store error so that we can easily determine error/warn
                   a) came via error handler
                   b) calling info
              */
              $this->error = $error;
              $errInfo = $error['typeStr'].': '.$error['file'].' (line '.$error['line'].')';
              $errMsg = $error['message'];
              if ($error['type'] & $this->debug->getCfg('errorMask')) {
                  $this->debug->error($errInfo.': ', $errMsg);
              } else {
                  $this->debug->warn($errInfo.': ', $errMsg);
              }
              $error['continueToNormal'] = false; // no need for PHP to log the error, we've captured it here
              $error['inConsole'] = true;
              // Prevent ErrorHandler\ErrorEmailer from sending email.
              // Since we're collecting log info, we send email on shutdown
              $error['email'] = false;
              $this->error = null;
          } elseif ($this->debug->getCfg('output')) {
              $error['email'] = false;
              $error['inConsole'] = false;
          } else {
              $error['inConsole'] = false;
          }
      }
docs: errorHandler.error event subscriber
  adds error to console as error or warn
  
  @param Event $error error/event object
  
  @return void