Truthy and falsy

Like most computer languages, Twig supports boolean data types and so everything has an inherent boolean value, known as truthy and falsy.

Even though an attribute/object may not be boolean it will still be truthy in a conditional.

For example,

{% if product.description %}
    <div>
        {{ product.description|raw }}
    </div>
{% endif %}

returns...

<div>
    <p>These nike air max trainers are great.</p>
</div>

As long as a product description is set.

Checking whether an attribute/object is truthy can avoid empty HTML tags.

The rules to determine if an expression is true or false are the same as in PHP; here are the edge case rules: