public function render()
    {
        // get messages
        $allMessages = [
            'danger'  => array_unique(
                array_merge(
                    $this->flashMessenger->getErrorMessages(),
                    $this->flashMessenger->getCurrentErrorMessages()
                )
            ),
            'success' => array_unique(
                array_merge(
                    $this->flashMessenger->getSuccessMessages(),
                    $this->flashMessenger->getCurrentSuccessMessages()
                )
            ),
            'warning' => array_unique(
                array_merge(
                    $this->flashMessenger->getWarningMessages(),
                    $this->flashMessenger->getCurrentWarningMessages()
                )
            ),
            'info'    => array_unique(
                array_merge(
                    $this->flashMessenger->getInfoMessages(),
                    $this->flashMessenger->getCurrentInfoMessages()
                )
            ),
            'default' => array_unique(
                array_merge(
                    $this->flashMessenger->getMessages(),
                    $this->flashMessenger->getCurrentMessages()
                )
            ),
        ];

        // clear messages
        $this->flashMessenger->clearMessagesFromContainer();
        $this->flashMessenger->clearCurrentMessagesFromContainer();

        // initialize output
        $output = '';

        // loop through messages
        foreach ($allMessages as $groupKey => $groupMessages) {
            foreach ($groupMessages as $message) {
                $addClass = $groupKey == 'default' ? '' : 'alert-' . $groupKey;

                // setup view model
                $viewModel = new ViewModel();
                $viewModel->setVariable('alertClass', $addClass);
                $viewModel->setVariable('alertMessage', $message);
                $viewModel->setTemplate('zfrapid-library/widget/bootstrap-alert');

                // add rendered output
                $output .= $this->getView()->render($viewModel);
            }
        }

        // return output
        return $output . "\n";
    }