A region is a rectangle, polygon, or ellipse or a combination of two or more of these shapes. The SetWindowRgn function sets the window region of a window.
The window region determines the area within the window where the system permits drawing. In other words, parts of the form beyond the region are not visible. Any mouse clicks on invisible parts pass through them to the windows beneath.
Basically, the demo brings up a form with a left to right series of "holes" (white, round circles, each an inch or so in diameter) with the circles showing whatever is behind them (that is, through the "holes" they form)
It gets cooler when you move the demo form around and realize that the holes are showing stuff on your screen that"s behind the form (took a minute to figure that out because I first ran it on an empty screen background <s>).
One of the more imaginative things I"ve come across in form design in a while.
Credits: PHP (4.4.9), an HTML-embedded scripting language,
MySQL (5.1.55-log), the Open Source standard SQL database,
AceHTML Freeware
Version 4, freeware HTML Editor of choice. Hosted by Korax Online Inc.
How to create transparent areas inside a form -- punching holes in the form 
