How to get event if my window is covered

[Lord]

I think my stupid fault was to make #InfoWindow a "StickyWindow".
Here I had tried to circumvent the z-order problem with gadgets.
It didn't came to my mind, that #InfoWindow would also be above any other window.
And yes, I was seeking for an event that occurs if my #MainWindow was covered.
But I can live with the found solution.

[BarryG]

Re-visiting this topic. How can I tell if my window is 100% covered by another one? I was going to try JHPJHP's code but it's not in the archive I downloaded from him.