Structs
ISO 8601 combined date and time with time zone.
ISO 8601 time duration with nanosecond precision.
This also allows for the negative duration; see individual methods for details.
The time zone with fixed offset, from UTC-23:59:59 to UTC+23:59:59.
Enums
A description of what went wrong with the push notification.
Referred from Firebase documentation
Fatal errors. Referred from Firebase
documentation