content: sub mapState(fx)
      m.global.observeField("state", "_mapStateHandler")
      m._mapStateImplementation = fx
  end sub
  
  sub _mapStateHandler()
      props = m._mapStateImplementation(m.global.state, m.global.prevState)
      if props <> invalid then setState(props) else ?"IGNORED GLOBAL STATE CHANGE"
  end sub
  