Metaclass system
- Moose is built on top of Class::MOP, also writen by Stevan Little
- A meta object protocol is an API to a language's object system
- Class::MOP is heavliy based on CLOS (Common Lisp Object System) and its meta object system.
- Art of the Metaobject Protocol (Gregor Kiczales, Jim Des Rivieres, Daniel G. Bobrow, Jim Des Rivieres)