Probably depends on your situation.  FYI, the semantics don't seem to be
   documented:  The swap device(s) with the lowest number will be completely
   filled before the device(s) with the next higher number see any paging
   activity.  (This is based on my observations of swapctl -l over time.)

that's wrong and right.  swapctl defines what the priority is under the
`SWAP OPTIONS' section you noted:

     priority=N      This option sets the priority of the specified swap de-
                     vice to N.  The highest priority is 0, second priority is
                     1, etc.

but your observations are correct.



FWIW, i agree with scott about fstab(5)/swapctl(8)/mount(8), and have
fixed fstab(5) to refer to other pages (and updated it a bit).