a "feature"*. Explained in <https://m.youtube.com/watch?v=HNEm8zmkjBU>
it is the exact same binary-incompatibility issue faced by Power ISA
on its 32- to 64-bit transition: 32-bit hardware was **unable** to
-trap-and-emulate 64-bit binarues because the opcodes were (are) the same.
+trap-and-emulate 64-bit binaries because the opcodes were (are) the same.
It is therefore *guaranteed* that extensions to the register file
width and quantity in Simple-V shall only be made in future by