In order to clarify the intellectual property license granted with Contributions from any person or entity, Orbeon must have a Contributor License Agreement (CLA) on file that has been signed by each Contributor, indicating agreement to the license terms below. This license is for your protection as a Contributor as well as the protection of Orbeon and its users; it does not change your rights to use your own Contributions for any other purpose.
If you plan to submit contributions to Orbeon, please download, review, sign and return a copy of the Orbeon Contributor License Agreement.
It's enough if you want to make changes and distribute them on your own, but it's not enough if you want your changes to become contributions included as part of the main Orbeon Forms source code repository and distributions.
This wikipedia page provides some general information about CLAs and mentions some major projects which require CLAs.
The Django project has a FAQ in which covers the reasons they have a CLA.