Twig: Add a class if a string containers a descender

_helpers.html

{# If str contains a character with descender ('gjpqy'), outputs a class #}

{% macro descender_class(str) %}
    {% set chars = [ 'g', 'j', 'p', 'q', 'y'] %}
    {% set hasDescender = false %}
    {% for c in chars %}
        {% if c in str %}
          {% set hasDescender = true %}
        {% endif %}
    {% endfor %}
    {% if hasDescender %}
      has-descender
    {% endif %}
{% endmacro %}

template.html

{% import "_helpers" as helpers %}

<h1 class="{{ helpers.descender_class(entry.myHeading) }}">
  {{ entry.myHeading }}
</h1>