Fare_zone vs. fee_zone for public transit stops

Hi folks,
After I searched the forum and the wiki about the fare_zone and fee_zone tag, I ended up being confused.

Is there a state of the art best practice today about how a add fare zones of public transit networks to public transit stops?

I would like to figure out which of the 2 tags fit most and if I add them to the node, way or relation of the stop.

Any thought?

Cheers!