{% macro b(class=None, tag="div", id=None) -%}
<{{ tag }}
{%- if class is not none %} class="{{class}}" {%- endif -%}
{%- if id is not none %} id="{{id}}" {%- endif -%}
>
{%- if caller %}
    {{ caller() }}
{% endif -%}
</{{ tag }}>
{%- endmacro %}