z-order:
As you can see in the picture the big Knob is overlapping another widget.
This way it is not possible to control the lowest widget.
With the new version you can move back the big widget
z-order: to answer your question, each widget has a focus which his always a rectangle.
So in special situations the z-order helps when you need place on the screen because of many widgets.
Panel Widgets:
In my use case I created 2 Panel widgets, one is green and the other is red.
I perfectly overlapped the 2 and in scripting I am shown the green or the red.
This way on conjunction with the on beat changed event I built a visual metronome.
I’m having issues with the z-order: If I have placed a panel widget over a knob widget (using bring to front), when I next open GP, the panel is always behind the knob. I’m assuming the z-order of every widget should be saved and recalled exactly as it was when you saved the gig file?
@pianopaul how are you using scripting to show/hide the green or red panels?