This reminds me of how when Apple created the UI for the Lisa (and then the Mac), they thought that on the original Xerox Alto, windows could overlap, so Quickdraw had to handle overlapping windows [0]: “Smalltalk didn't even have self-repairing windows - you had to click in them to get them to repaint, and programs couldn't draw into partially obscured windows. Bill Atkinson did not know this, so he invented regions as the basis of QuickDraw and the Window Manager so that he could quickly draw in covered windows and repaint portions of windows brought to the front.”<p>I thought I read somewhere that Jobs specifically asked for this, (mis)remembering having seen it at PARC, but I cannot find the quote at the moment.<p>[0] <a href="http://www.folklore.org/StoryView.py?project=Macintosh&story=On_Xerox,_Apple_and_Progress.txt" rel="nofollow">http://www.folklore.org/StoryView.py?project=Macintosh&story...</a>