Firmhouse makes use of Liquid, an open-source template language which provides a safe way to generate user content. This way, you can configure/edit appearance of your Checkout, Self Service Center and add dynamic content to emails and webhooks.
Why should I use Liquid?
You want to allow your users to edit the appearance of your application, but don't want them to run insecure code on your server.
You want to render templates directly from the database.
You need a template engine which does HTML just as well as emails.