day represents a day of a month
. It normally holds values in the range 1 to 31,
but may hold non-negative values outside this range
. It can be constructed with any
unsigned value,
which will be subsequently truncated to fit into
day's unspecified internal storage
. day meets the
Cpp17EqualityComparable (Table
28)
and
Cpp17LessThanComparable (Table
29) requirements,
and participates in basic arithmetic with
days objects,
which represent a difference between two
day objects
.