anchor.diff:  
       let model' =
           match msg with
  +        | NoOp -> model
           | AddItem ->
               let maxId =
                   if model.Items |> List.isEmpty then 1
  
positive.code:                     onMouseClick (fun _ -> ClearCompleted)]
                  [ text "Clear completed" ] ]
  
  let todoHeader model =
      header
          [attribute "class" "header"]
  
negative.code:                     |> List.map (fun x -> x.Id)
                      |> List.max
              (fun items ->
                  items @ [{  Id = maxId + 1
                              Name = model.Input
                              Done = false
                              IsEditing = false}])
              |> updateItems {model with Input = ""}
          | ChangeInput v -> {model with Input = v}
          | MarkAsDone i ->
  