When /someone/ wishes /thing/ is highlighted /color/ & /thing/ has region /region/ {
    # it's not really correct to just stick a side-effect in the
    # When handler like this. but we did it in Realtalk, and it
    # was ok, so whatever for now
    Display::fillRect device $x $y [expr {$x+$width}] [expr {$y+$height}] $color
}