anchor.diff:  
       let MouseWheelEvent =
           Class "MouseWheelEvent"
  -        |=> Inherits Event
  +        |=> Inherits MouseEvent
           |+> Instance [
                   "wheelDelta" =@ T<int>
                   "initMouseWheelEvent" =>
  
positive.code:             ]
      let CompositionEvent =
          Class "CompositionEvent"
          |=> Inherits Event
          |+> Instance [
                  "data" =@ T<string>
                  "initCompositionEvent" =>
  
negative.code:                     T<int>?detailArg ^-> T<unit>
              ]
  
      let FocusEvent =
          Class "FocusEvent"
          |=> Inherits UIEvent
          |+> Instance [
              "relatedTarget" =@ EventTarget
          ]
  
      let MouseEvent =
          Class "MouseEvent"
          |=> Inherits UIEvent
          |+> Instance [
                  "altKey" =@ T<bool>
                  "button" =@ T<int> // short
  