anchor.diff:  
       let MouseWheelEvent =
           Class "MouseWheelEvent"
  -        |=> Inherits Event
  +        |=> Inherits MouseEvent
           |+> Instance [
                   "wheelDelta" =@ T<int>
                   "initMouseWheelEvent" =>
  
positive.code: 
      let WheelEvent =
          Class "WheelEvent"
          |=> Inherits Event
          |+> Instance [
                  "deltaX" =@ T<int>
                  "deltaY" =@ T<int>
  
negative.code:                 I.Event
                  I.EventTarget
                  I.CustomEvent
                  I.FocusEvent
                  I.DocumentEvent
                  I.DocumentView
                  I.AbstractView
  