NSDocument is not in the responder chain

Question

According to the doc (cf. fig 1.10), the NSDocument should be in the responder chain.

However, if I try to log the responder chain via the method

- (IBAction)logResponderChain:(id)sender
{
    NSResponder *responder = self.view;
    while ((responder = [responder nextResponder])) {
        NSLog(@"%@", responder);
    }
}

here what I get:

2014-04-16 13:04:16.228 MyApp[5430:303] < NSWindow: 0x6080001e3200>

2014-04-16 13:04:16.228 MyApp[5430:303] < NSWindowController: 0x608000085dc0>

Why is it so? Am I missing something?

The application in which I have this issue is a minimal document-based application: there is nothing except the logging method.