Gets the chronology of this period, which is the ISO calendar system.
!(p)
The {@code Chronology} represents the calendar system _in use.
The ISO-8601 calendar system is the modern civil calendar system used today
_in most of the world. It is equivalent to the proleptic Gregorian calendar
system, _in which today's rules for leap years are applied for all time.
Gets the chronology of this period, which is the ISO calendar system. !(p) The {@code Chronology} represents the calendar system _in use. The ISO-8601 calendar system is the modern civil calendar system used today _in most of the world. It is equivalent to the proleptic Gregorian calendar system, _in which today's rules for leap years are applied for all time.
@return the ISO chronology, not null