-where 0 <= MVL <= XLEN and vlen may come from an immediate, `RA`, or from the `CTR` SPR,
-depending on options set with the `setvl` instruction.
+where 0 <= MVL <= 127 and vlen may come from an immediate, `RA`, or from the `CTR` SPR,
+depending on options selected with the `setvl` instruction.
+
+Programmer's Note: understanding of Cray-style Vectors is far beyond the scope
+of the Power ISA Technical Reference. Guidance on the Cray Vector paradigm is
+best sought elsewhere: good studies include Academic Courses given on the 1970s
+Cray Supercomputers over the past 30 years.