{% set attr = attr|merge({ 'class': attr.class|default('') ~ ' modal' }) %}
<div{% for attrname, attrvalue in attr %} {{ attrname }}="{{- attrvalue -}}"{% endfor %}>
    <div class="modal-header">
        {% block header %}{% endblock %}
    </div>
    <div class="modal-body">
        {% block body %}{% endblock %}
    </div>
    <div class="modal-footer">
        {% block footer %}{% endblock %}
    </div>
</div>