Valid `[$url]` rule with regexp considered as invalid

```
Error: "'url' is not valid modifier" in the rule: "[$url=/^https?:\/\/\d{1\,3}\.\d{1\,3}\.\d{1\,3}\.\d{1\,3}\/.*(\?|&)__cpo=aHR0c/]#%#//scriptlet('set-constant', '__Cpn.prototype.showAds', 'false')"
Error: "'url' is not valid modifier" in the rule: "[$url=/^https?:\/\/\d{1\,3}\.\d{1\,3}\.\d{1\,3}\.\d{1\,3}\/.*(\?|&)__cpo=aHR0c/]#%#//scriptlet('abort-on-stack-trace', 'addEventListener', '/attachEvent[\s\S]*?Popup[\s\S]*?register/')"
```