anchor.diff:  
       let KeyboardEvent =
           Class "KeyboardEvent"
  -        |=> Inherits Event
  +        |=> Inherits UIEvent
           |+> Instance [
                   "altKey" =@ T<bool>
                   "ctrlKey" =@ T<bool>
  
positive.code:                     T<int>?detailArg ^-> T<unit>
              ]
  
      let MouseEvent =
          Class "MouseEvent"
          |=> Inherits Event
          |+> Instance [
                  "altKey" =@ T<bool>
                  "button" =@ T<int> // short
  
negative.code:                 I.Event
                  I.EventTarget
                  I.CustomEvent
                  I.FocusEvent
                  I.DocumentEvent
                  I.DocumentView
                  I.AbstractView
  