<B>Note:B> This is a new module is a new addition to Data::FormValidator and is
should be considered Beta.
This constraint creates a regular expression based on the format string
passed in to validate your date against. It understands the following symbols:
Y year (numeric)
M month (numeric)
D day (numeric)
Other parts of the string become part of the regular expression, so you can
do perlish things like this to create more complex expressions:
Internally Date::Calc is used to test the functions.