I have the form on my page with text `url` field. User can input there any value, like:

* <http://example.com/forum/viewtopic.php?t=557761&sid=daea20300c8eea4681fd1d87aa76c622>
* <http://www.example.com/forum/viewtopic.php?t=557761&sid=daea20300c8eea4681fd1d87aa76c622>
* www.example.com/forum/viewtopic.php?t=557761&z=123456
* example.com/forum/viewtopic.php?t=557761&sid=daea20300c8eea4681fd1d87aa76c622
* 557761

How can I validate that correct domain is given (`example.com`) and then extract topic id (`557761`)?

Looks like I should use `jQuery.isNumeric` first (to capture last case), if it is not numeric, then I can extract the value like `/^.*t=(\d+)$/`. But how should I check the domain in the regex?