This project is used to build the Symfony Documentation both in https://symfony.com and the Continuous Integration service used in the Symfony Docs repository.
This project is considered an internal tool and therefore, you shouldn't use this project in your application. Unlike the rest of the Symfony projects, this repository doesn't provide any support and it doesn't guarantee backward compatibility either. Any or the entire project can change, or even disappear, at any moment without prior notice.
If you are looking for a project to build your reStructuredText documentation in PHP, use Doctrine RST parser (which is also used by this project internally).