QuickForm->Addrule->Regular Expression->URL check!

Hi I'm trying to compose a regular expression to check an URL via the QuickForm rules. Unfortunately I can't seem to get the regexp entirely correct :-( The check shouldn't be thorough in the sense that it should only catch really bad URLs - it shouldn't be so strict that correct URL's could be rejected! I've tried using something like the following: $this->registerRule('url', 'regex', '/^(file|ldap|http|https|ftp)://(([-a-z0-9])+\.)+([a-z]{2,6}|([a-z/]+[a-z/]{2,6}))$/'); but it creates javascript errors when trying to do client-side validation! I guess because the format isn't entirely correct! Do any of you have any suggestions for an URL-checker which isn't to strict? Regards, Tommy Ipsen