You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/eclipse-ee4j/ee4j-website - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/ee4j - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/.github - Project repository hosted on GitHub.
https://github.com/jakartaee/.github - Project repository hosted on GitHub.