To create a new validation you should use AbstractValidator as it implements most of the common methods and properties.

The validation should happen at IsValid, and if the validator can configure a client-side validation script, it should use the SupportsBrowserValidation to indicate that it does support client-side validation and also implement the ApplyBrowserValidation(BrowserValidationConfiguration, InputElementType, IBrowserValidationGenerator, IDictionary, String) to configure it.