Determine whether a YYYY-MM-DD string names a date that exists in the Gregorian calendar.
Only the calendar is checked: the string must already have the YYYY-MM-DD shape. Century years
are leap years only when divisible by 400, so 2000-02-29 exists and 1900-02-29 does not.
Determine whether a YYYY-MM-DD string names a date that exists in the Gregorian calendar.
Only the calendar is checked: the string must already have the YYYY-MM-DD shape. Century years are leap years only when divisible by 400, so 2000-02-29 exists and 1900-02-29 does not.