All IRB Laws of the Game can be found here.
From time to time, National Unions request clarification of laws from the IRB. When the IRB completes the clarification, they distribute the document, and send back to all nations. These can be very important, as they clear up issues with laws and interpreation of laws. They must be read and understood, similar to actual laws, by coaches, players, referees, and spectators.
You can find a listing of all law clarifications here.