There aren't many rules for maintainers of Slim to remember; what we have is listed here.
Our code is better if more than one set of eyes looks at it. Therefore we do not merge our own pull requests unless there is an exceptional circumstance. This helps to spot errors in the patch and also enables us to share information about the project around the maintainer team.
Sometimes it's helpful to collaborate on a patch before it's ready to be merged. We use the text WIP (for Work in Progress) in the title to mark these PRs.
If a PR has WIP in its title, then it is not to be merged. The person who raised the PR will remove the WIP text when they are ready for a full review and merge.
By ensuring that all merged PRs are assigned to a milestone, we can easily find which PRs were in which release.