Filtering elements by attribute value

Let's say you have a list of Book elements (like here), each of which have a title, author and category fields. Now if on a page you want to show a filtered list of only the books from category Fiction, you can do this:

{% elementscontext category="Fiction" %}
  <h2>Fiction books</h2>
  <ul>
    {% for fiction_book in elements %}
      <li><b>{{ fiction_book.title }}</b> by {{ fiction_book.author }}</li>
    {% endfor %}
  </ul>
{% endelementscontext %}

This will give you only the books from category Fiction:

Fiction books

• The Abilene Trail by Ralph Compton and Dusty Richards
• Across the Nightingale Floor by Liam Hearn
• The accidental by Ali Smith