Branch is the one and only place where the Scalar
(non-prefixed) operations differ from the Vector (element)
-instructions, as explained in a separate section.
+instructions (as explained in a separate section) although
+a case could be made for the perspective that they are identical,
+but the defaults for new parameters in the Scalar case makes branch
+identical to Power ISA v3.1 Scalar branches.
+
The
RM bits can be used for other purposes because the Arithmetic modes
make no sense at all for a Branch.