Controleert de geldigheid van de date gevormd door de argumenten.
Day is binnen het toegestane aantal dagen voor de gegeven month .
Schrikkeljaren zijn in overweging genomen. It eats nearly every kind of date correctly. So if you use a DB, it is not so a bad idea to use the routines from it, cause the routines in the DB also can correct the year. Because checkdate accepts years between 0 and 32767 inclusive, you may want to include a cutoff year in your code when checking dates entered in a form by users. Currently there is no validation of the values in month or day.