Region codes are actually implemented as a single 8-bit byte, with each bit corresponding to a region. The bit is clear if a disc can be played in that region, else it is set. Thus, a region 1 disc has a region code of 0xFE.
It is possible for a disc to be multi-region, and work in a set of territories. "Region 0" is not a region at all, but a combination of all 8 regions, expressed using a region code of 0x00.