You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/jakartaee/jakartaee-documentation - Project repository hosted on GitHub.
https://github.com/jakartaee/jakartaee-documentation-playbook - Project repository hosted on GitHub.
https://github.com/jakartaee/jakartaee-tutorial - Project repository hosted on GitHub.
https://github.com/jakartaee/jakartaee-documentation-ui - Project repository hosted on GitHub.