Notes:
* **PO9**-PO1 Prefixed-Prefixed (96-bit) instructions are prohibited. EXT1xx is
- thus inherently Unvectorizable as the EXT1xx prefix is 32-bit
- on top of an SVP64 prefix which is 32-bit on top of a Defined Word-instruction
- and the complexity at the Decoder becomes too great for High
+ thus inherently Unvectorizable as the complexity at the Decoder of recognising
+ `{PO1-word}{PO9-word}{Defined-word-instruction}` becomes too great for High
Performance Multi-Issue systems.
* There is however no reason why PO9-PO1 (EXT901?) as an entirely new RESERVED
64-bit Encoding