..caution::

Prior to 2.8, templates in custom namespaces are not pre-compiled by

Symfony's cache warmup process. They are compiled on demand. This may

cause problems if two simultaneous requests are trying to use the

template for the first time.

The registered namespace is called ``foo_bar``, which refers to the

``vendor/acme/foo-bar/templates`` directory. Assuming there's a file

called ``sidebar.twig`` in that directory, you can use it easily: