anchor.diff:  /// Specialized to Nu's specific use case by not providing a TryGetValue but rather ContainsKey and GetValue since Nu
   /// uses them separately. A more general implementation would only provide ToSeq and TryGetValue.
   type [<NoEquality; NoComparison>] MapGeneralized =
  -    { ToKeys : List<IComparable>
  +    { ToKeys : IComparable List
         ContainsKey : IComparable -> bool
         GetValue : IComparable -> obj }
   
  
positive.code:       SplashImageOpt : Image AssetTag option }
  
  /// Describes the shape of a desired overlay.
  type [<StructuralEquality; StructuralComparison>] OverlayNameDescriptor =
      | NoOverlay
      | RoutedOverlay
      | DefaultOverlay
  
negative.code: 
  /// The type of a screen transition. Incoming means a new screen is being shown, and Outgoing
  /// means an existing screen being hidden.
  type [<StructuralEquality; NoComparison; Struct>] TransitionType =
      | Incoming
      | Outgoing
  
  /// The state of a screen's transition.
  type [<StructuralEquality; NoComparison; Struct>] TransitionState =
      | IncomingState
      | OutgoingState
      | IdlingState
  
  /// Describes one of a screen's transition processes.
  /// TODO: figure out if this really needs to be CLIMutable.
  type [<NoEquality; NoComparison; CLIMutable>] Transition =
      { TransitionType : TransitionType
        TransitionLifeTime : int64
  