Close Current Window
The following code closes the current window.
To see this code in action, check out the "close" link on this popup page:
(then close it using its "Close" link in the top right corner)
Close Another Window
You can also close another window. That is, a different window to the one that the "Close" button is located on.
Note that you may need to click "Close Popup Window" twice - the first click will bring this window back into focus and the second click will click the actual button.