diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/DefaultTextRunTypographyProperties.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/DefaultTextRunTypographyProperties.cs
index f2e9fca09d..a725417b3e 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/DefaultTextRunTypographyProperties.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/DefaultTextRunTypographyProperties.cs
@@ -12,115 +12,158 @@ namespace ICSharpCode.AvalonEdit.Rendering
 	/// </summary>
 	public class DefaultTextRunTypographyProperties : TextRunTypographyProperties
 	{
+		/// <inheritdoc/>
 		public override FontVariants Variants {
 			get { return FontVariants.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool StylisticSet1 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet2 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet3 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet4 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet5 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet6 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet7 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet8 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet9 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet10 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet11 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet12 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet13 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet14 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet15 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet16 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet17 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet18 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet19 { get { return false; } }
+		/// <inheritdoc/>
 		public override bool StylisticSet20 { get { return false; } }
 		
+		/// <inheritdoc/>
 		public override int StylisticAlternates {
 			get { return 0; }
 		}
 		
+		/// <inheritdoc/>
 		public override int StandardSwashes {
 			get { return 0; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool StandardLigatures {
 			get { return true; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool SlashedZero {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontNumeralStyle NumeralStyle {
 			get { return FontNumeralStyle.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontNumeralAlignment NumeralAlignment {
 			get { return FontNumeralAlignment.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool MathematicalGreek {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool Kerning {
 			get { return true; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool HistoricalLigatures {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool HistoricalForms {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontFraction Fraction {
 			get { return FontFraction.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontEastAsianWidths EastAsianWidths {
 			get { return FontEastAsianWidths.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontEastAsianLanguage EastAsianLanguage {
 			get { return FontEastAsianLanguage.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool EastAsianExpertForms {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool DiscretionaryLigatures {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override int ContextualSwashes {
 			get { return 0; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool ContextualLigatures {
 			get { return true; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool ContextualAlternates {
 			get { return true; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool CaseSensitiveForms {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override bool CapitalSpacing {
 			get { return false; }
 		}
 		
+		/// <inheritdoc/>
 		public override FontCapitals Capitals {
 			get { return FontCapitals.Normal; }
 		}
 		
+		/// <inheritdoc/>
 		public override int AnnotationAlternates {
 			get { return 0; }
 		}
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs
index 2482f16f1a..6687c3a1f2 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs
@@ -696,10 +696,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				throw new ArgumentException("Cannot dispose visual line because it is in construction!");
 			}
 			visibleVisualLines = null;
-			visualLine.IsDisposed = true;
-			foreach (TextLine textLine in visualLine.TextLines) {
-				textLine.Dispose();
-			}
+			visualLine.Dispose();
 			RemoveInlineObjects(visualLine);
 		}
 		#endregion
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLine.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLine.cs
index fb0f0133d7..2dce9c29a0 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLine.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLine.cs
@@ -23,9 +23,18 @@ namespace ICSharpCode.AvalonEdit.Rendering
 	/// </summary>
 	public sealed class VisualLine
 	{
+		enum LifetimePhase : byte
+		{
+			Generating,
+			Transforming,
+			Live,
+			Disposed
+		}
+		
 		TextView textView;
 		List<VisualLineElement> elements;
 		internal bool hasInlineObjects;
+		LifetimePhase phase;
 		
 		/// <summary>
 		/// Gets the document to which this VisualLine belongs.
@@ -47,10 +56,18 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		/// </summary>
 		public ReadOnlyCollection<VisualLineElement> Elements { get; private set; }
 		
+		ReadOnlyCollection<TextLine> textLines;
+		
 		/// <summary>
 		/// Gets a read-only collection of text lines.
 		/// </summary>
-		public ReadOnlyCollection<TextLine> TextLines { get; private set; }
+		public ReadOnlyCollection<TextLine> TextLines {
+			get {
+				if (phase < LifetimePhase.Live)
+					throw new InvalidOperationException();
+				return textLines;
+			}
+		}
 		
 		/// <summary>
 		/// Gets the start offset of the VisualLine inside the document.
@@ -99,6 +116,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		
 		internal void ConstructVisualElements(ITextRunConstructionContext context, VisualLineElementGenerator[] generators)
 		{
+			Debug.Assert(phase == LifetimePhase.Generating);
 			foreach (VisualLineElementGenerator g in generators) {
 				g.StartGeneration(context);
 			}
@@ -108,8 +126,13 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				g.FinishGeneration();
 			}
 			
+			var globalTextRunProperties = context.GlobalTextRunProperties;
+			foreach (var element in elements) {
+				element.SetTextRunProperties(new VisualLineElementTextRunProperties(globalTextRunProperties));
+			}
 			this.Elements = elements.AsReadOnly();
-			CalculateOffsets(context.GlobalTextRunProperties);
+			CalculateOffsets();
+			phase = LifetimePhase.Transforming;
 		}
 		
 		void PerformVisualElementConstruction(VisualLineElementGenerator[] generators)
@@ -168,14 +191,13 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			}
 		}
 		
-		void CalculateOffsets(TextRunProperties globalTextRunProperties)
+		void CalculateOffsets()
 		{
 			int visualOffset = 0;
 			int textOffset = 0;
-			foreach (VisualLineElement element in Elements) {
+			foreach (VisualLineElement element in elements) {
 				element.VisualColumn = visualOffset;
 				element.RelativeTextOffset = textOffset;
-				element.SetTextRunProperties(new VisualLineElementTextRunProperties(globalTextRunProperties));
 				visualOffset += element.VisualLength;
 				textOffset += element.DocumentLength;
 			}
@@ -185,6 +207,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		
 		internal void RunTransformers(ITextRunConstructionContext context, IVisualLineTransformer[] transformers)
 		{
+			Debug.Assert(phase == LifetimePhase.Transforming);
 			foreach (IVisualLineTransformer transformer in transformers) {
 				transformer.Transform(context, elements);
 			}
@@ -197,11 +220,50 @@ namespace ICSharpCode.AvalonEdit.Rendering
 					}
 				}
 			}
+			phase = LifetimePhase.Live;
+		}
+		
+		/// <summary>
+		/// Replaces the single element at <paramref name="elementIndex"/> with the specified elements.
+		/// The replacement operation must preserve the document length, but may change the visual length.
+		/// </summary>
+		/// <remarks>
+		/// This method may only be called by line transformers.
+		/// </remarks>
+		public void ReplaceElement(int elementIndex, params VisualLineElement[] newElements)
+		{
+			ReplaceElement(elementIndex, 1, newElements);
+		}
+		
+		/// <summary>
+		/// Replaces <paramref name="count"/> elements starting at <paramref name="elementIndex"/> with the specified elements.
+		/// The replacement operation must preserve the document length, but may change the visual length.
+		/// </summary>
+		/// <remarks>
+		/// This method may only be called by line transformers.
+		/// </remarks>
+		public void ReplaceElement(int elementIndex, int count, params VisualLineElement[] newElements)
+		{
+			if (phase != LifetimePhase.Transforming)
+				throw new InvalidOperationException("This method may only be called by line transformers.");
+			int oldDocumentLength = 0;
+			for (int i = elementIndex; i < elementIndex + count; i++) {
+				oldDocumentLength += elements[i].DocumentLength;
+			}
+			int newDocumentLength = 0;
+			foreach (var newElement in newElements) {
+				newDocumentLength += newElement.DocumentLength;
+			}
+			if (oldDocumentLength != newDocumentLength)
+				throw new InvalidOperationException("Old elements have document length " + oldDocumentLength + ", but new elements have length " + newDocumentLength);
+			elements.RemoveRange(elementIndex, count);
+			elements.InsertRange(elementIndex, newElements);
+			CalculateOffsets();
 		}
 		
 		internal void SetTextLines(List<TextLine> textLines)
 		{
-			this.TextLines = textLines.AsReadOnly();
+			this.textLines = textLines.AsReadOnly();
 			Height = 0;
 			foreach (TextLine line in textLines)
 				Height += line.Height;
@@ -456,7 +518,20 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		/// <summary>
 		/// Gets whether the visual line was disposed.
 		/// </summary>
-		public bool IsDisposed { get; internal set; }
+		public bool IsDisposed {
+			get { return phase == LifetimePhase.Disposed; }
+		}
+		
+		internal void Dispose()
+		{
+			if (phase == LifetimePhase.Disposed)
+				return;
+			Debug.Assert(phase == LifetimePhase.Live);
+			phase = LifetimePhase.Disposed;
+			foreach (TextLine textLine in TextLines) {
+				textLine.Dispose();
+			}
+		}
 		
 		/// <summary>
 		/// Gets the next possible caret position after visualColumn, or -1 if there is no caret position.
@@ -567,6 +642,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		
 		internal VisualLineDrawingVisual Render()
 		{
+			Debug.Assert(phase == LifetimePhase.Live);
 			if (visual == null)
 				visual = new VisualLineDrawingVisual(this);
 			return visual;