``html_classes`` ================ The ``html_classes`` function returns a string by conditionally joining class names together: .. code-block:: html+twig <p class="{{ html_classes('a-class', 'another-class', { 'errored': object.errored, 'finished': object.finished, 'pending': object.pending, }) }}">How are you doing?</p> .. note:: The ``html_classes`` function is part of the ``HtmlExtension`` which is not installed by default. Install it first: .. code-block:: bash $ composer require twig/html-extra Then, on Symfony projects, install the ``twig/extra-bundle``: .. code-block:: bash $ composer require twig/extra-bundle Otherwise, add the extension explicitly on the Twig environment:: use Twig\Extra\Html\HtmlExtension; $twig = new \Twig\Environment(...); $twig->addExtension(new HtmlExtension());