Right now the process of updating old rulesets to ensure they have sufficient test coverage is very tedious. Typically one has to pull out a list of hostnames from deeply nested regexes like this one:

<rule from="^http://s3(?:-website)?(-ap-(?:nor|sou)theast-1|-(?:eu|us)-west-\d|-external-\d|-sa-east-1)?\.amazonaws\.com/"                                                     

Instead, it would be nice to automatically extract hostnames from regexes when possible. The Python exrex module claims to do this. We could write a script that would do use that module to extract hostnames where possible and add them to <target host=...> tags.

Of course, we can't extract hostnames from wildcard matches like \w+, but that's fine. We'll have to manually add test cases for those.