Hi Martijn, thanks for your response!
I'm currently looking at something like this...
**user-agent: *** #disallowing page.php and any parameters after it
disallow: /page.php #but leaving anything that starts with par1=ABC
allow: /page.php?par1=ABC
I would have thought that you could disallow things broadly like that and give an exception, as you can with files in disallowed folders. But it's not passing Google's robots.txt Tester.
One thing that's probably worth mentioning really is that there are only two variables that I want to allow of the par1 parameter. For example's sake, ABC123 and ABC456. So would need to be either a partial match or "this or that" kinda deal, disallowing everything else.