Timetable Modification: Section Members

We can't expect schools to have their timetables 100% complete on the first day of the school-year, as changes are inevitable we need to allow at least some degrees of freedom.

We want to allow changes to members of a section in a reliable manner, so that it would propagate to Attendance and Gradebooks properly without losing any data.

Currently - when you add or remove a member, no information about when you did it is stored. IRelationshipAdded IRelationshipRemoved events are fired, so you can hook into them.

In the future we would like to:
 keep date added, date removed information about section members in the section.
 allow querying for members during specific periods in time.
 add event types for member move actions.