comes when Pack/Unpack are enabled, and it is really important
to be aware how the Arrays of vec2/3/4 become re-ordered
*and swizzled at the same time*.
+
+Pack/Unpack applies to
+[[sv/mv.vec]] as well however the uniform relationship and
+the fact that the source and destination subvector length
+must be the same (vec2/3/4) makes things slightly easier to
+understand. The main thing to keep in mind about Pack/Unpack
+is that it engages a swap of the ordering of the VL-SUBVL
+nested for-loops, in exactly the same way that Matrix REMAP
+can do. When Pack or Unpack is enabled it is the SUBVL for-loop
+thar becomes outermost.