anchor.diff:                  | _ -> None
   
           and set v = current.Value <- v
  +        
  +    [<CLIEvent>]
  +    static member ContextError = contextError.Publish
   
       member x.GetProcAddress(name : string) =
           (handle |> unbox<IGraphicsContextInternal>).GetAddress(name)
  
positive.code:         match ContextHandle.Current with
              | Some handle -> handle.ReleaseCurrent()
              | _ -> ()
  
          handle.MakeCurrent(window)
          ContextHandle.Current <- Some x
  
          GLVM.hglCleanup((unbox<IGraphicsContextInternal> handle).Context.Handle)
  
negative.code: open OpenTK.Graphics.OpenGL4
  open Aardvark.Base
  
  type ContextErrorEventArgs(msg : string) =
      inherit EventArgs()
  
      let mutable retry = false
      member x.Retry 
          with get() = retry
          and set (value : bool) = retry <- value
  
      member x.Message = msg
  
  type ContextErrorEventHandler =
      delegate of obj * ContextErrorEventArgs -> unit
  
  /// <summary>
  /// a handle represents a GL context which can be made current and released
  