4.23. Creating and Applying Patches
For open source projects (like this one) everyone has read access to the repository, and anyone can make a contribution to the project. So how are those contributions controlled? If just anyone could commit changes, the project would be permanently unstable and probably permanently broken. In this situation the change is managed by submitting a patch file to the development team, who do have write access. They can review the patch first, and then either submit it to the repository or reject it back to the author.
Patch files are simply Unified-Diff files showing the differences between your working copy and the base revision.