Staff is a member of the course staff. Depending on course settings, they
may have permission to see the data of all users, and to edit the information of other
users.
Student is a student participating in the class. They can only see their
own information, and can do assessments.
None is a user who at one point was part of the course but is no longer
enrolled in the course or part of the staff. They can no longer access the course but
their work done within the course has been retained.