There is a contradiction between your description of what you want and the example you provide: in the example, the "<url>" pattern is found and, according to your stated rules, no substitution whatsoever should occur. It seems that your example probably makes clearer what you want, but you are failing to describe your needs correctly in plain English words. If you can't explain it in literary language, then you probably don't really understand what you are trying to do. And this might be the key to your problem.