The include statement includes a template and returns the rendered content of that file into the current namespace:

<t:include from="header.html"/>
<t:include from="footer.html"/>

A little bit different syntax to include a template can be:

<div class="content" t:include="news.html">
    <h1>Fake news content</h1>
    <p>Lorem ipsum</p>

In this case, the content of div will be replaced with the content of template ‘news.html’.

You can add additional variables by passing them after the with attribute:

<t:include from="header.html" with="{'foo': 'bar'}"/>

You can disable the access to the current context by using the only attribute:

<t:include from="header.html" with="{'foo': 'bar'} only="true"/>
You can mark an include with the ignore-missing attribute in which case Twital
will ignore the statement if the template to be included does not exist.
<t:include from="header.html" with="{'foo': 'bar'} ignore-missing="true"/>

ignore-missing can not be an expression; it has to be evauluated only at compile time.

To use Twig expressions as template name you have to use a namespace prefix on ‘form’ attribute:

<t:include t:from="ajax ? 'ajax.html' : 'not_ajax.html' " />
<t:include t:from="['one.html','two.html']" />


For more information about the include tag, please refer to Twig official documentation.