Hi Alan,
In general, the user who should be able to edit a post created by another user would require the edit_others_posts capability. Note that this would apply to all posts that the user can access. For example, you could create a group which has the following capabilities:
- edit_posts
- edit_published_posts
- publish_posts
- edit_others_posts
The Roles and Capabilities documentation has details on each of those.
Beyond that, it would be great to be able to determine these things in a more fine-grained manner, we’re headed in that direction but object-based capabilities aren’t supported yet. Anyhow, the above might be suitable for your case. You can give it a try and determine the most suitable set of capabilities.
I’ll mark this one as resolved, but feel free to comment if there are further questions or ideas you’d like to share on this topic.