This is incorrect. Quoting @cpennington above it should say something like:

> For courses that include a module that is set up to test multiple variants, all event types include special a field in the `context`. The field is called `course_user_tags`, and it contains a dictionary with all of the tags for that user in that course (from the `user_api_usercoursetag` table, with the same keys and values as in the table). It can be used to to identify the student's assigned partition and group.

It would be useful to add a link or mention to look at the documentation of `user_api_usercoursetag`. 

As a side comment, it looks like `course_user_tags` may be used in the future for other things beside A/B testing. @cpennington  are there any `keys` there that are specific to A/B testing? We should probably mention them here.