Supervisor.init

You're seeing just the callback init, go back to Supervisor module for more information.

init(init_arg)

init(init_arg :: term()) ::
  {:ok, {:supervisor.sup_flags(), [:supervisor.child_spec()]}} | :ignore

Callback invoked to start the supervisor and during hot code upgrades.

Developers typically invoke Supervisor.init/2 at the end of their init callback to return the proper supervision flags.