1. Scope
The packages are MIT-licensed. Contributions are accepted under the same licence, which for most projects of this size makes a separate signed agreement unnecessary.
2. What you confirm by contributing
That you wrote the contribution or have the right to submit it, and that you are willing for it to be published under the project’s licence. Where an employer owns your work, that permission has to come from them rather than from you.
3. What a contribution includes
Code, tests and documentation together. A change that alters behaviour without a test that would fail on the old behaviour is incomplete, and a change that alters a documented contract without updating the document is also incomplete.
4. Review
Contributions are reviewed adversarially: the reviewer’s job is to try to refute the change rather than to approve it. That is not a comment on the contributor — it is the only way to catch decisions that no test can fail.
5. What is not accepted
Dependencies in the element package. It takes none by design, and a contribution that adds one belongs in the content package or nowhere.