Debugging Twig
Poor man's debug
This will print all the keys of all data available. We don't print value
as that can sometimes throw a fatal error in Drupal b/c it's trying to access a private property or class.
<ol>
{% for key,value in _context %}
<li>{{ key }}</li>
{% endfor %}
</ol>
Full JSON output
<pre><code>{{ _context|json_encode(constant('JSON_PRETTY_PRINT')) }}</code></pre>
Be careful with a full _context
output as that can be crazy in Drupal, often it's best to dump specific variables.