When I added a sheet to display on top of TableFlips’ document, I wondered why the text field appear disabled, tabbing through elements didn’t work, and overall functionality was limited to accepting click events: It turned out you have to make sure that you disable most of the NSWindow settings in Interface Builder except the title bar (NSTitledWindowMask). Only with a title bar (which is never visible in a sheet anyway) will the interaction work properly.

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