There are no "exact" limitations. Rather it has to do with the Bern convention allowing nations to restrict copyright protection in "special circumstances" tha

There are no "exact" limitations. Rather it has to do with the Bern convention allowing nations to restrict copyright protection in "special circumstances" that don't "unduly" interfere with "normal" exploitation of the work by the rights-holder. In other words it allows nations to pass laws relating to what constitutes fair use. I would assume that absent this sort of thing the Bern convention would allow the WTO to impose sanctions on any nation that decided we were right regarding Oracle v. Google, Sony v. Connectix, etc.