| Class | DuplicatePriorityError | Undocumented |
| Class | FeatureRuleSource | Access feature rule sources from the database or elsewhere. |
| Class | StormFeatureRuleSource | Access feature rules stored in the database via Storm. |
| Class | MemoryFeatureRuleSource | Access feature rules stored in non-persistent memory. |
| Class | NullFeatureRuleSource | For use in testing: everything is turned off |