It isn't as much a regulation problem as much as a definitional problem. How do you define "porn" or whatever material requires the xxx designation? I've stumbled across sites that have an adult content warning, which I don't know if it is required for their content or not. Perhaps if it is, there's your answer -- anything with an adult content warning = XXX. I think what some people might not like is sites that might have nude pictures (i.e. photo sites or nudist sites) being required to be a XXX.
I don't know how to define it, but I know it when I see it. :-)
Seriously though, it would be no different than how it is defined for movies, magazines, etc. Obviously that has to be some definition for those.
> It isn't as much a regulation problem as much as a definitional problem. How do you define "porn" or whatever material requires the xxx designation?
Maybe...it's pron if you have to pay for it?