The article below mentions only %%partition

https://docs.mongodb.com/realm/rules/expressions/#sync-expansions

It should also include %%user in the list to make it consistent with the following:

https://docs.mongodb.com/realm/sync/data-access-patterns/permissions/#permissions

Your rule expressions can use JSON expansions like %%partition and %%user to dynamically determine a user's permissions based on the context of their request.