It can represent values in the range [min(), max()].
It can be constructed with any int value,
which will be subsequently truncated to fit into year's unspecified internal storage.
year meets the Cpp17EqualityComparable (Table Clause 28)
and Cpp17LessThanComparable (Table Clause 29) requirements,
and participates in basic arithmetic with years objects,
which represent a difference between two year objects.