Since any register group is somehow special, "special register groups" are just an ambiguous concept that can be passively misunderstood to "obviously" mean wha

Since any register group is somehow special, "special register groups" are just an ambiguous concept that can be passively misunderstood to "obviously" mean whatever register classification one finds important, not actively "stretched" to take on new meanings. Other commonplace "special" register groups include special purpose vs general purpose (SP, BP etc. vs AX to DX on early X86), different sizes, mutually exclusive overlays (e.g. FPU and MMX registers on X86).