tillda, if you wouldn’t mind, I would prefer if changes you plan to contribute are posted as attachments to a specific feature request or bug task in our bug tracker, and include the complete files that were modified in a tar.gz or .zip format. Since we use SVN for all our development work, I simply place your changed files in, update from the repository to merge the changes, test, and check-in once I’ve confirmed it works.
This diff files do make it nice to see the changes, but it would actually be more work for me to use those to consider your contributions. And as a lazy programmer, I don’t like more work.
All that aside, thanks for your earnest interest and self-initiative in contributing to MODx. We certainly appreciate it, and your contributions just may earn you a spot on the MODx core team. Who knows...?
Cheers