gistfile1.mustache

<!-- new_base.html -->

<header>
{% block header %}
{% endblock %}
</header>

<main id="content" class="group" role="main">
{% block main %}
    <div id="main-container" class="main-container container">
    {% block content %}{% endblock %}
    </div>
{% endblock %}
</main>

<footer>
{% block footer %}
{% endblock %}
</footer>

gistfile2.mustache

<!-- old_base.html -->

<header>
{% block header %}
{% endblock %}
</header>

<div id="main-container" class="main-container container">
    {% block main %}
        {% block content %}{% endblock %}
    {% endblock %}
</div

<footer>
{% block footer %}
{% endblock %}
</footer>