GFW itself is a not a law though. And IMO it'd be a bad idea to make GFW as if itself was a law. That would give the GFW operators way too much power. In civil laws, it should be as clear and specific as possible to tell the public what they cannot do.
One of the worst aspects of GFW is that it has never been made clear what traffic it will bock. Censorship without transparency is one kind of 不教而诛 (penalty without reason).
The GFW is part of the Chinese legal framework on the regulation of the internet. In particular, it ensures two things:
1. Data on Chinese citizens must be physically stored within Chinese borders.
2. Content that violates Chinese laws cannot be displayed or disseminated on the Chinese internet.
The GFW will block traffic to sites whose owners violate above stipulations. It could be failing to store user data in China, or disseminating pornographic, violent, or seditious content.
I think this spells out pretty clearly what is and isn't allowed.