You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/eclipse-ee4j/jaxb-ri - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jaxb-istack-commons - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jaxb-dtd-parser - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jaxb-fi - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jaxb-stax-ex - Project repository hosted on GitHub.