/// <summary>
        /// Synchronises the shapes in the candidate slide with the shapes in the reference slide.
        /// Adds any shape that exists in the reference slide but is missing in the candidate slide.
        /// </summary>
        private static void SyncShapesFromReferenceSlide(PowerPointSlide refSlide, PowerPointSlide candidate, List<string> markedForDeletion)
        {
            if (refSlide == null || candidate == null || refSlide == candidate)
            {
                return;
            }

            DeleteShapesMarkedForDeletion(candidate, markedForDeletion);

            candidate.CopyBackgroundColourFrom(refSlide);
            candidate.Layout = refSlide.Layout;
            candidate.Design = refSlide.Design;

            // synchronize extra shapes other than visual items in reference slide
            var candidateSlideShapes = candidate.GetNameToShapeDictionary();
            var extraShapes = refSlide.Shapes.Cast<Shape>()
                                             .Where(shape => !PowerPointSlide.IsIndicator(shape) &&
                                                             !PowerPointSlide.IsTemplateSlideMarker(shape) &&
                                                             !candidateSlideShapes.ContainsKey(shape.Name))
                                             .Select(shape => shape.Name)
                                             .ToArray();

            if (extraShapes.Length != 0)
            {
                var refShapes = refSlide.Shapes.Range(extraShapes);
                CopyShapesTo(refShapes, candidate);
            }

            // synchronize shapes position and size, except bullet content
            candidateSlideShapes = candidate.GetNameToShapeDictionary();
            var sameShapes = refSlide.Shapes.Cast<Shape>()
                                            .Where(shape => !PowerPointSlide.IsIndicator(shape) &&
                                                            !PowerPointSlide.IsTemplateSlideMarker(shape) &&
                                                            candidateSlideShapes.ContainsKey(shape.Name));

            var shapeOriginalZOrders = new SortedDictionary<int, Shape>();
            foreach (var refShape in sameShapes)
            {
                var candidateShape = candidateSlideShapes[refShape.Name];
                Graphics.SyncWholeShape(refShape, ref candidateShape, candidate);

                shapeOriginalZOrders.Add(refShape.ZOrderPosition, candidateShape);
            }

            SynchroniseZOrders(shapeOriginalZOrders);
        }