Gets the era applicable at this date.
!(p)
The official ISO-8601 standard does not define eras, however {@code IsoChronology} does.
It defines two eras, 'CE' from year one onwards and 'BCE' from year zero backwards.
Since dates before the Julian-Gregorian cutover are not _in line with history,
the cutover between 'BCE' and 'CE' is also not aligned with the commonly used
eras, often referred to using 'BC' and 'AD'.
!(p)
Users of this class should typically ignore this method as it exists primarily
to fulfill the {@link ChronoLocalDate} contract where it is necessary to support
the Japanese calendar system.
@return the IsoEra applicable at this date, not null
Gets the era applicable at this date. !(p) The official ISO-8601 standard does not define eras, however {@code IsoChronology} does. It defines two eras, 'CE' from year one onwards and 'BCE' from year zero backwards. Since dates before the Julian-Gregorian cutover are not _in line with history, the cutover between 'BCE' and 'CE' is also not aligned with the commonly used eras, often referred to using 'BC' and 'AD'. !(p) Users of this class should typically ignore this method as it exists primarily to fulfill the {@link ChronoLocalDate} contract where it is necessary to support the Japanese calendar system.
@return the IsoEra applicable at this date, not null