Loop through a particular category (or tag) with Jekyll/Siteleaf

category-loop1.html

{% for post in site.posts %}
  {% if post.categories contains 'Foo' %}
  <li>{{ post.title }}</li>
  {% endif %}
{% endfor %}

category-loop2.html

{% assign posts = site.posts | where_exp: "post", "post.categories contains 'Foo'" %}
{% for post in posts %}
  <li>{{ post.title }}</li>
{% endfor %}