jekyll/docs/_includes/docs_option.html

{% for item in include.items %}
  {% assign p = site.documents | where: "url", item.link | first %}
  <option value="{{ p.url }}">
    {% if p.menu_name %}
      {{ p.menu_name }}
    {% else %}
      {{ p.title }}
    {% endif %}
  </option>
{% endfor %}