>>>Anyway, I'm looking for a definition of a url format (ie structure and valid chars) Once I have that I may have a go at it
>>
>>Ok, I'll post a reference to that thread in a second - give me 2 minutes.
>
>
>I think this defines the valid format http://www.w3.org/Addressing/URL/url-spec.html

Yes, but too complex for me. Good luck!