different Defined Words be allocated within any `EXT{z}` prefixed
or unprefixed space for a given value of `z`. Even if UnVectoriseable
an instruction Defined Word space must have the exact same Instruction
-and exact same Instruction Encoding in all spaces or not be allocated at all.
-This is required as an inviolate hard rule governing Primary Opcode 9*
+and exact same Instruction Encoding in all spaces (including
+being RESERVED if UnVectoriseable) or not be allocated at all.
+This is required as an inviolate hard rule governing Primary Opcode 9
+that may not be revoked under any circumstances*
# Remapped Encoding (`RM[0:23]`)