Part of lp.registry.interfaces
| Class | BugNotificationLevel | Bug Notification Level. |
| Class | BlueprintNotificationLevel | Bug Notification Level. |
| Interface | IStructuralSubscription | A subscription to a Launchpad structure. |
| Interface | IStructuralSubscriptionTarget | A Launchpad Structure allowing users to subscribe to it. |
| Interface | IStructuralSubscriptionForm | Schema for the structural subscription form. |
| Class | DeleteSubscriptionError | Delete Subscription Error. |
| Class | UserCannotSubscribePerson | User does not have permission to subscribe the person or team. |