Hello @e-d
I don't think this particular parameter has been documented (yet) for the LAN PoE module. It has for some of the newer COMX modules which also can be powered externally.
Another reason, I guess, is, that with M5Stack devices (Fire, Gray, Base) there is no need to switch between output and input as they use a different electrical circuit than M5Core2, which allows the power pin to be both (input and output) at the same time.
As for learning about these parameters - sometimes looking at the Arduino libraries and / or schematic helps figuring out how things are meant to work.
Thanks
Felix