Pro PHP and jQuery by Jason Lengstorf.pdf - Computer Science ...

CHAPTER 9 ■ PERFORMING FORM VALIDATION WITH REGULAR EXPRESSIONS
Armed with this regex pattern, you can now validate the date input in your application.
Adding a Validation Method to the Calendar Class
To validate the date string, you will add a new private method to the Calendar class called _validDate().
This method will accept the date string to be validated, then compare it to the validation pattern
using preg_match(), which returns the number of matches found in the given string. Because this
particular pattern will only match if the entire string conforms to the pattern, a valid date will return 1,
while an invalid date will return 0.
If the date is valid, the method will return TRUE; otherwise, it will return FALSE.
Add this method to the Calendar class by inserting the following bold code into
class.calendar.inc.php: