http:// prefix - Not a valid URL.

Making critical - since this bug prevents entry of any offsite URLs (not just ones with a protocol).

Here is a patch that fixes the problem. It also has improved the regex to function correctly for the mailto: protocol, since that does not include the '//' delimiter.

Looks good, is the line "+print $external_pattern . $end;" debugging code?

Whoops!
Yes - that can be taken out :)

Sorry about the delay on this patch! It really was quite a show-stopper!

Anyway, I found that your patch didn't actually help with mailto: since email addresses still don't fit the rest of the regular expression. I simply changed

  '/^(' . $allowed_protocols . ':\/\/)?'.

to

  '/^((' . $allowed_protocols . '):\/\/)?'.

Since the last protocol was being checked with the :// and the rest weren't. Released as version 1.2 on Drupal.org