Twig template code - Displaying flash messages using bootstrap

gistfile1.twig

{# twig template #}

<div class="flash-messages">
    {% block flashes %}
        {% for notice_level in ['success','error','info', 'warning', 'notice'] %}
            {% if app.session.hasFlash(notice_level) %}
                <div class="alert alert-{{ notice_level }}">
                  <a class="close" data-dismiss="alert" href="#">x</a>
                  <h4 class="alert-heading">{{ notice_level }}</h4>
                  {{ app.session.flash(notice_level) }}
                </div>
            {% endif %}
        {% endfor %}
    {% endblock flashes %}
</div>