src/Debug/Output/Html.php
protected function processAlerts()
    {
        $errorSummary = $this->errorSummary->build($this->debug->internal->errorStats());
        if ($errorSummary) {
            \array_unshift($this->data['alerts'], array(
                'alert',
                array($errorSummary),
                array(
                    'class' => 'danger error-summary',
                    'dismissible' => false,
                )
            ));
        }
        return parent::processAlerts();
    }
protected function processAlerts()
    {
        $errorSummary = $this->errorSummary->build($this->debug->internal->errorStats());
        if ($errorSummary) {
            \array_unshift($this->data['alerts'], array(
                'alert',
                array($errorSummary),
                array(
                    'class' => 'danger error-summary',
                    'dismissible' => false,
                )
            ));
        }
        return parent::processAlerts();
    }
process alerts

@return string