Find the regex used by HTML5 forms for validation

Question

Some HTML5 input elements accept the pattern attribute, which is a regex for form validation. Some other HTML5 input elements, such as, input type=email

Answer 1

The HTML5 spec currently lists a valid email address as one matching the ABNF:

1*( atext / "." ) "@" ldh-str *( "." ldh-str )

which is elucidated in this question. @SLaks answer provides a regex equivalent.

That said, with a little digging through the source, shows that WebKit implemented email address validation using basically the same regex as SLaks answer, i.e.,

[a-z0-9!#$%&'*+/=?^_`{|}~.-]+@[a-z0-9-]+(\.[a-z0-9-]+)*

However, there is no requirement that email addresses be validated by a regex. For example, Mozilla (Gecko) implemented email validation using a pretty basic finite state machine. Hence, there needn't be a regex involved in email validation.