Most interactive Versor commands should have, as the outermost level
of their body, the macro versor-as-motion-command, which
handles the block cursor (selection highlighting). in the code within
versor-as-motion-command, you can call
versor-set-current-item, passing in the beginning and end of
the new selection, and the new selection will be displayed
automatically at the end of versor-as-motion-command. If you do
not call versor-set-current-item,
versor-as-motion-command will try to work out an appropriate
selection for the current dimension.
If you want a multipart selection, you can call
versor-set-current-items, passing in a list of conses of start
and end positions, or a list of overlays.