The following code example uses the derived class Text Box and validates an e-mail address that the user enters.
If the e-mail address is not in the standard format (containing "@" and "."), the validation fails, an Error Provider icon is displayed, and the event is canceled.
And after all, you don't want to reinvent the wheel, do you?
"But aren't there already a ton of validation plugins out there?
Controlling the Text Box using the keyup function is a bad idea because the user may copy/paste the text inside the Text Box or choose one of the browser's autocomplete fields, etc.