-The xext proposal defines a small number N (e.g. N= 8) standardised R-type instructions
-xcmd0, xcmd1, ...xcmd[N-1], preferably in the brownfield opcode space.
+The overloadable opcode (or xext) proposal allows a non standard extension to use a documented 20 + 3 bit (or 52 + 3 bit on RV64) UUID identifier for an instruction for _software_ to use. At runtime, a cpu translates the UUID to a small implementation defined 12 + 3 bit bit identifier for _hardware_ to use. It also defines a fallback mechanism for the UUID's of instructions the cpu does not recognise.
+
+Tl;DR see below for a C description of how this is supposed to work.
+
+It defines a small number N standardised R-type instructions
+xcmd0, xcmd1, ...xcmd[N-1], preferably in the brownfield opcode space. We usually assume N = 8 (aka log2(8) = 3 in the + 3 above).