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I have a document-based app that is not using NSDocument subclasses (basically writing all the MDI support myself).

I got bitten because I added a document getter to my window controller. Apparently the window calls something like

[self windowController] document] isDocumentEdited]

although the document message in the window controller class is said only to return id. The result is used for handling the responder chain (i.e. sending a message to nil will reach the document of the current window, if no-one else responds to the message. This should not require that the instance be (a subclass of) [[NSDocument).

Can anyone give more details about what is really required by the document returned? I would prefer to use the name of document for my getter, and I could just implement isDocumentEdited This seems quite risky, since others might perhaps also make unjustified assumptions about the type of the result.