EggData and CoordinateSystem

I have created a plane with EggData and save it to a file use writeEgg.

If found that the coordinate system is not defined in the egg file and the system seems thought that it is Y-up.

How can I make the egg file starts with
{ Z-Up }

I want to try the setCoordinateSystem api but CoordinateSystem class has not much document to follow.

open the egg file in a texteditor and replace Y-up with Z-up

The enum is global:

from pandac.PandaModules import CSYupRight
eggData.setCoordinateSystem(CSYupRight)

It works, thank you.