Why does NSString respond to appendString?

Question

I was playing with the respondsToSelector method in Objective-C on MacOS-X 10.6.7 and Xcode 4.0.2, to identify if an object would respond to certain messages. According to t

Answer 1

You should not make assumptions about a method being not there. That method might be used internally or for whatever reason it exists. Technically, it's just private API.

You only have a contract to the public declarations (docs), and they don't show that message. So be prepared to get into trouble rather quickly if you use other features.