I think that the concept is old and developed enough now that a company like Apple should come up with some clear guidelines on how these lists should be used and how they should behave. Unfortunately that is not the case and even within Apple’s stock of applications you won’t find two in which the source lists behave the same. So it’s really hard to learn what you can expect a source list to do.

What does sending a message to nil do in Objective-C? What value does it return? You probably know that if the method is declared to return an object, you get back nil, but what if the method is declared to return a char? An int? A long long? A float? A struct? And how does it all work?