views/tag/field/help.html
{% macro parse(name, help, errors, errorClass) %}
{% if help or errors[name] %}
<span class="help-block">
{% if help %}{{ help | safe }}{% endif %}
{% if errors[name] %}
<span class="{{ errorClass or 'error' }}">{{ errors[name].message or errors[name] }}</span>
{% endif %}
</span>
{% endif %}
{% endmacro %}