A year-month _in the ISO-8601 calendar system, such as {@code 2007-12}. !(p) {@code YearMonth} is an immutable date-time object that represents the combination of a year and month. Any field that can be derived from a year and month, such as quarter-of-year, can be obtained. !(p) This class does not store or represent a day, time or time-zone. For example, the value "October 2007" can be stored _in a {@code YearMonth}. !(p) 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. For most applications written today, the ISO-8601 rules are entirely suitable. However, any application that makes use of historical dates, and requires them to be accurate will find the ISO-8601 approach unsuitable.