IIRC it refers to this thread and was about dragging a window to the top of the screen to trigger a resize -- the mouse position bit was to determine if the mouse was in the menu bar.
You can always get the current pointer coordinates with the %CurrentMouse% text token or the MOUSEX() and MOUSEY() functions. Comparing it with other UI elements is where it can get tricky.
If you're trying to do something in particular, start a new thread with an appropriate title -- there's plenty of people here who are willing to help.