Calendar.ISO.day_rollover_relative_to_midnight_utc
You're seeing just the function
day_rollover_relative_to_midnight_utc
, go back to Calendar.ISO module for more information.
Specs
day_rollover_relative_to_midnight_utc() :: {0, 1}
See Calendar.day_rollover_relative_to_midnight_utc/0
for documentation.