The Calendar week represents a standard time period of
a week. In the Gregorian calendar, the standard week
starts on a sunday and ends on a saturday; in the ISO
calendar, it starts on a monday and ends on a sunday.
The week are might not be aligned to the year, and thus
the week may cross year borders and the year of
the week might not be the same as the year of all the
days in the week. The basic rule is that the week year
is the year that has the most days in the week, but
since week number only is specified in the ISO calendar
- and derivates - the week number of most calendars
is the week number of most of the days in the ISO
calendar, which modifies this rule for the Gregorian calendar;
the week number and year is the same as for the ISO calendar,
except for the sundays.
When adding, moving and subtracting months
to a week, it falls back to using days.
When adding, moving or subtracting years,
if tries to place the moved week in the
resulting year.
Calendar.YMD.Hour()->parse()