 1. If anything goes wrong, check the popup window/console. It should tell you where the code is
    that caused the error.
 2. Error handling is useful to create more stable scripts.
 3. Don't call repaint functions such as window.Repaint() in callback function on_size() {},
    especially in pseudo transparent mode.
 4. Don't try to assign parameter "gr" from function on_paint(gr) {} with other value, nor try
    to store "gr" in another variable.
 5. Consider using Dispose() methods where you can to free up memory. See interfaces.txt for
    where it's supported.
 6. Remember to retrieve window width and height in on_size() callback, because their values
    during startup is not reliable.
 7. It's NOT recommended to create objects in callback function on_paint(), since it will be
    called frenquently.
