I don’t think a domain option would be necessary because even that has limitations, like, do you match sub domains or not? Then maybe you will have to support wildcards, dot prefixes, etc.
So I would say a function that receives the url and returns a list of attributes would likely be enough. The default is to return an empty list - the current behavior - and then people can customize it to consider the domain, sub domains, etc.
But regarding your main request, I don’t have a need for it right now. 
