The 'regions' used in QuickDraw are an amazing (for their time) data structure, a testament to the genius of Bill Atkinson. I strongly recommend reading the patent to see how cool and useful they were to the original Mac windowing system (http://patentdetails.patenttools.com/patent/04622545?searchi... click on the 'download pdf' link in the top left).
Steve Jobs know how important regions were: http://www.folklore.org/StoryView.py?project=Macintosh&s...