content: sub init()
      m.top.observeField("on", "updateOff")
  end sub
  
  ' boolean interface fields default to "false" not "invalid"
  ' we can set "off" based on "on" being set, 
  ' and then in our button check both 
  ' ex: on = false and off = false means nothing has been set
  sub updateOff(event as object)
      on = event.getData()
      if on = true then
          m.top.off = false
      else
          m.top.off = true
      end if
  end sub