In Drupal you use this delimiter to perform actions like adding classes to a template depending on a template variable, applying conditional rules for rendering items (like if-else blocks), displaying page regions if they are not empty, etc.

Example: Check if a theme region exists before displaying it.

 {% if page.sidebar_second %}
   <div>{{ page.sidebar.second }}</div>
 {% endif %}

Conditional region display:

{% if is_admin %}
  <div class = "admin-only-block">{{ admin_block }}</div>
  {% endif %}

Removing Whitespace:

{% spaceless %}{% endspaceless %}

This removes all non-text whitespace between HTML tags excluding spaces inside blocks of text or space inside an HTML tag.

To trim leading or trailing whitespace on either side of Twig delimiters insert a hyphen within the delimiter: {%- variable -%}