GenServer.format_status

You're seeing just the callback format_status, go back to GenServer module for more information.
Link to this callback

format_status(reason, pdict_and_state)

View Source (optional)

Specs

format_status(reason, pdict_and_state :: list()) :: term()
when reason: :normal | :terminate

Invoked in some cases to retrieve a formatted version of the GenServer status.

This callback can be useful to control the appearance of the status of the GenServer. For example, it can be used to return a compact representation of the GenServer's state to avoid having large state terms printed.

pdict_and_state is a two-elements list [pdict, state] where pdict is a list of {key, value} tuples representing the current process dictionary of the GenServer and state is the current state of the GenServer.