pdnew/themes/default/templates/form/fieldset.html

<fieldset
    {% if content.id %}
        id="{{ content.id }}"
    {% endif %}
    class="{{ content.css_classes }}"
>

    {% block intro %}
        {% if content.intro %}
            <div class="intro">
                {{ content.intro }}
            </div>
        {% endif %}
    {% endblock %}

    {% block fields %}
        {% if content.fields_pending_render|length %}
            <div class="fields">
                {% for field in content.fields_pending_render %}
                    {{ field.render() }}
                {% endfor %}
            </div>
        {% endif %}
    {% endblock %}

    {% block buttons %}
        {% if content.buttons|length %}
            <div class="buttons">
                {% for button in content.buttons_pending_render %}
                    {{ button.render() }}
                {% endfor %}
            </div>
        {% endif %}
    {% endblock %}

</fieldset>