{% def vanilla_nav_node(item) %}
{% let children = item.children ?? () %}
{% let href = item.href ?? '' %}
{% let title = item.title ?? 'Untitled' %}
<li>
  {% if href %}<a href="{{ href }}"{% if item.active ?? false %} aria-current="page"{% end %}>{{ title }}</a>{% else %}<span>{{ title }}</span>{% end %}
  {% if children %}
  <ul>
    {% for child in children %}{{ vanilla_nav_node(child) }}{% endfor %}
  </ul>
  {% end %}
</li>
{% end %}
{% for item in nav_items ?? () %}{{ vanilla_nav_node(item) }}{% endfor %}