Hi, I would like to describe some additional behavior for objects when they are interacting with another objects. The prime example is GTInspector; by default to add presentation you implement a method with "gtInspectorPresentationOrder:". This is fine if there is just one method like this, but when the object can serve multiple purposes it can quite mess up the protocol (in my opinion). Example of that could be (Spec) TreeModel; there are many methods like menu:, displayBlock:, childrenBlock: etc. that should be different based on the particular object. However having a method for each of those cases in the observed method is just a mess. So how could one approach this? The first thing that comes to my mind is a visitor. That might possibly work for code that I've written, but not for spotter/inspector as they work directly on the target object. Thanks, Peter