How to understand data from fit file

Hello,

I try to understand some data of my last fit file  but I did not found any documentation about this.

For exemple the event type "rider_change_position" take data value 0, 1, 2 or 3. How to understand the meaning  of this values ?

Also:

There is an event_type "marker" with event "55" and data withe values 0,5,8 or 11  ? What is it ?

Regards