If is the conditional block — its contents are rendered only if the condition is true.
{% if editmode or previewmode %} Visible for logged in users {% else %} Visible for everyone else {% endif %}
There are {% if count < 5 %}less than{% elsif count > 5 %}more than{% else %}exactly{% endif %}5 items.
Some examples on how to work with different kind of conditions:
{% if element.email != '' %} {{ element.email }} {% endif %} {% if element.name == 'peter' and element.name != 'John' %} Hello you, Non-John Peter! {% endif %} {% if articles.size < 1 %} No articles to display {% endif %} // Check if array contains desired value, e.g. ['foo', 'bar'] {% if array contains 'foo' %} There is a 50/50 chance that this array also contains "bar" :) {% endif %} // Check if string contains desired value, e.g 'hello world' {% if some_string contains 'hello' %} String contains "hello" {% endif %}