What happens if two ObjC categories override the same method?

I know of a couple of rules regarding Objective-C categories:

1. Category methods should not override existing methods (class or instance)
2. Two different categories implementing the same method for the same class will result in undefined behavior

I would like to know what happens when I override one of my own category methods in the same category. For example:

@interface NSView (MyExtensions)
- (void)foo; // NSView category implementation
@end

@interface MyClass : NSView
{ }
@end

@interface MyClass (MyExtensions)
- (void)foo; // MyClass category implementation
@end

With these interfaces defined, which method will be executed when I run the following code?

MyClass * instance = [[MyClass alloc] initWith...];
[instance foo];
[instance release];

Note: With my compiler, the MyClass implementation takes precedence, but I'm not sure if that is guaranteed to occur, or simply one specific flavor of undefined behavior.