There are several different types of validation controls. Each performs a specific type of validation when the form is updated.
Right-click on the validation control and select Properties from the shortcut menu.
Set the ControlToValidate to txtBirthday.
Change the Type from String to Date.
Set the MinimumValue to 1/1/1880.
Set the MaximumValue to 1/1/2009.
Set the ErrorMessage to Please select a credible birthday.
If we return to our birthday page in our web browser, we see that if we enter a spurious date such as
1/1/1850 and then press Enter to cause a postback, the validation kicks in and we are greeted with an error message.