Adds the specified validation server control to the System.Web.UI.ValidatorCollection collection.
When added to the System.Web.UI.ValidatorCollection collection of a System.Web.UI.Page object through the Page.Validators property, the System.Web.UI.IValidator implementation takes part in validation. Its IValidator.Validate method is called together with the IValidator.Validate methods of all other validators. All validators then share in determining whether the System.Web.UI.Page object as a whole is valid.