For example on the Windows version of Photoshop I can press Alt -> I -> A -> C in order to get to brightness/contrast. In my experience, by default, pressing the Alt key on the Mac version does not put the focus on the top menu (though I have been successful in clicking the top with the mouse and using the keyboard from there). I'm specifically referring to the ability to access the top of the menu using one keyboard button press, not the ability to move around when you're already there.
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