Calendar.TimeZoneDatabase.time_zone_period_from_utc_iso_days

You're seeing just the callback time_zone_period_from_utc_iso_days, go back to Calendar.TimeZoneDatabase module for more information.
Link to this callback

time_zone_period_from_utc_iso_days(arg1, arg2)

View Source (since 1.8.0)

Specs

time_zone_period_from_utc_iso_days(Calendar.iso_days(), Calendar.time_zone()) ::
  {:ok, time_zone_period()}
  | {:error, :time_zone_not_found | :utc_only_time_zone_database}

Time zone period for a point in time in UTC for a specific time zone.

Takes a time zone name and a point in time for UTC and returns a time_zone_period for that point in time.