CancelException vs OperationCanceledException

at LayoutHelpers.cs I see:

#if SILVERLIGHT
        /// <summary>
        /// Calculates the graph layout
        /// </summary>
        /// <exception cref="CancelException">Thrown when the layout is canceled.</exception>
#else
        /// <summary>
        /// Calculates the graph layout
        /// </summary>
        /// <exception cref="System.OperationCanceledException">Thrown when the layout is canceled.</exception>
#endif
        public static void CalculateLayout...

but this causes warning:

Warning 5   XML comment on 'Microsoft.Msagl.Miscellaneous.LayoutHelpers.CalculateLayout(Microsoft.Msagl.Core.Layout.GeometryGraph, Microsoft.Msagl.Core.Layout.LayoutAlgorithmSettings, Microsoft.Msagl.Core.CancelToken)' has cref attribute 'CancelException' that could not be resolved  .....\automatic-graph-layout\GraphLayout\msagl\Miscellaneous\LayoutHelpers.cs   34  30  msaglsilverlight

I don't understand why a conditional is used there for Silverlight, since
https://msdn.microsoft.com/en-us/library/system.operationcanceledexception(v=vs.95).aspx
says there is an OperationCanceledException for Silverlight 5 (maybe that is older code that wanted to support Silveright 4? I don't see any need to still support SL4, esp. since MoonLight is now totally obsolete and PipeLight has been released [http://pipelight.net/cms/about.html] for Linux)

Probably needs changes to other places CancelException is used in the code to use OperationCanceledException instead.

Anyway even if SL5 hadn't added that class, one could have added such class and if somewhere CancelException was thrown by internal system code, could catch it and rethrow it again as OperationCanceledException to keep the code cleaner

Start with LayoutHelpers.cs, especially the conditional XML documentation for CalculateLayout, then search the codebase for other uses of CancelException. Check the Silverlight-specific references and the compiler warning, and confirm that the completed change removes the unresolved cref warning while preserving the intended cancellation behavior.