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 now gives a (non-normative) regex which is supposed to exactly match all email addresses that it specifies as valid. There's a copy of it on my blog here: http://blog.gerv.net/2011/05/html5_email_address_regexp/ and in the spec itself: https://html.spec.whatwg.org/#e-mail-state-(type=email))

The version above is incorrect only in that it does not limit domain components to max 255 characters and does not prevent them beginning or ending with a "-".

Gerv