Provides "abilities". Those classes are best used via inheritance. They give extra functionality to a class.

The currently available abilities are:

• COMPARABLE for objects that can be compared between themselves;
• HASHABLE for objects that want to interact with the Garbage Collector when they are about to be collected;
• HASHABLE for objects that provide a hash-code (e.g. useful for hashed dictionaries and sets);
• OBSERVABLE for objects that can notify observers when their state changes (that's the Observer Design Pattern);
• STORABLE for objects that want to be put on an external medium, to be retrieved again later;
• VISITABLE for objects that can be visited using the Visitor Design Pattern.