How to ensure ONLY correct groups can be assigned to a task type

[Uncle Rob]

If you don't want to watch the video
1)  Create a group type on sys_user_group_type

1.5)  Copy the sys_id of the newly created sys_user_group_type
2)  Add the newly created group type to all the groups you want to assign that class of tasks to.
3)  Create a dictionary override on task.assignment_group.  
- Select the task table you want to control assignment groups for
- Select Override Reference Qualifier

- Set Reference Qualifier to type= sys_id of 1.5
4)  PROFIT!

How to ensure ONLY correct groups can be assigned to a task type