How to make sure latter popupPanel appear on top of preceding pupPanel

Scenario:
There might be cases the system requires a popupPanel from another popupPanel.
Sometimes, latter popupPanel may appears below the preceding popupPanel.

Resolution:
in such a situation, always  the z-index of the latter popupPanel higher than the previous popupPanel to ensure the latter popupPanel appears on top of the previous popupPanel.


code sample: