And what kind of form validation are you going to do with a regular expression? E-mail addresses like every other fool? (This is a the best to reject perfectly valid addresses because you baked unjustified assumptions in you regex)
https://html.spec.whatwg.org/#email-state-(type=email)
/^[a-zA-Z0-9.!#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/
What kind of validation are you going to do without a regular expression?
Actual form validation… I can't even think of a single kind of form validation where a regex would help…