{{html|replace({'{{region_top}}': region_top, '{{region_center}}': region_center})}}

{% set var = 'inner variable' %}
{{'this is a string with an {{var}}'|evaluate}}

$env = new Twig_Environment(new Twig_Loader_String());
echo $env->render(
  "Hello {{ name }}",
  array("name" => "World")
);

{% if attribute(array, key) is defined %}
    {{ attribute(array, key) }}
{% endif %}