Sounds like the open/closed principle of SOLID development. "Objects should be open to extension but closed to modification". This basically means that users of

Sounds like the open/closed principle of SOLID development. "Objects should be open to extension but closed to modification". This basically means that users of your code shouldn't have to modify your classes to add functionality. It should be done through inheriance and adding new types. http://en.wikipedia.org/wiki/Open/closed_principle http://en.wikipedia.org/wiki/Open/closed_principle