macOS Hillegass P 91

I've been messing around with this for days, so it's time to ask.
Hillegas's first challenge is this?

Create an application that can have only one window open, so it is not a document-based application.

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What puzzles me is the admonition that the window is to be of a certain type. I have googled/searched lists/ looked at the Apple Dev notes and I am sure it is there, but I am mystified **why** the challenge specifically mentions one window, and that it is **not** to be a document window. As far as I can tell, the other window is a simple application window, and this window already resides in the IB, but if someone can perhaps throw some light on this, or send a reference, I will be very appreciative.

HiRez said:

I don't think it's anything so mysterious, I believe he's just trying to tell you to create the project type as Cocoa Application instead of Cocoa Document-Based Application. Then your application will have one window associated with it (by default anyway), instead of one per open document.

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I dont't know the icon for embarrassment! Thanks...I did not even think of looking at the different types of applications! 🙂
Thanks