Briefly explain how the server control validation controls work?
A validation control works by evaluating the value of an input server control on the page to see whether it meets particular criteria. The input control to evaluate is specified by the validation controls Control To Validate attribute. You can programmatically cause a validation control to perform its evaluation by calling its Validate method, which sets the validation controls isValid property to true if validation succeeds and false if it fails. You can cause all of the validation controls on a page to validate their input controls by calling the Page. Validate method.