Video Layering
How video is layered in the output of the switcher depends on how an ME is re-entered onto the other, and what keyers are on-air for the ME.
If we assume that each ME has all keyers on-air and that ME 2 is re-entered into ME 1, and ME 1 is re-entered into ME P/P, the layering will start with ME 2 Background and progress to ME P/P and the highest keyer.