diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/OffsetChangeMap.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/OffsetChangeMap.cs
index 692b15e7b4..8612957a5b 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/OffsetChangeMap.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/OffsetChangeMap.cs
@@ -108,7 +108,7 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// <summary>
 		/// Gets the new offset where the specified offset moves after this document change.
 		/// </summary>
-		public int GetNewOffset(int offset, AnchorMovementType movementType)
+		public int GetNewOffset(int offset, AnchorMovementType movementType = AnchorMovementType.Default)
 		{
 			IList<OffsetChangeMapEntry> items = this.Items;
 			int count = items.Count;
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichText.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichText.cs
index 46fd4c9902..597bfe5015 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichText.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichText.cs
@@ -3,10 +3,12 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Windows.Documents;
+using ICSharpCode.AvalonEdit.Document;
 using ICSharpCode.AvalonEdit.Utils;
 
 namespace ICSharpCode.AvalonEdit.Highlighting
@@ -16,6 +18,11 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 	/// </summary>
 	public class RichText
 	{
+		/// <summary>
+		/// The empty string without any formatting information.
+		/// </summary>
+		public static readonly RichText Empty = new RichText(string.Empty);
+		
 		readonly string text;
 		internal readonly int[] stateChangeOffsets;
 		internal readonly HighlightingColor[] stateChanges;
@@ -53,6 +60,8 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		internal RichText(string text, int[] offsets, HighlightingColor[] states)
 		{
 			this.text = text;
+			Debug.Assert(offsets[0] == 0);
+			Debug.Assert(offsets.Last() <= text.Length);
 			this.stateChangeOffsets = offsets;
 			this.stateChanges = states;
 		}
@@ -191,9 +200,15 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// </summary>
 		public RichText Substring(int offset, int length)
 		{
-//			if (offset == 0 && length == this.Length)
-//				return this;
-			throw new NotImplementedException();
+			if (offset == 0 && length == this.Length)
+				return this;
+			string newText = text.Substring(offset, length);
+			RichTextModel model = ToRichTextModel();
+			OffsetChangeMap map = new OffsetChangeMap(2);
+			map.Add(new OffsetChangeMapEntry(offset + length, text.Length - offset - length, 0));
+			map.Add(new OffsetChangeMapEntry(0, offset, 0));
+			model.UpdateOffsets(map);
+			return new RichText(newText, model);
 		}
 		
 		/// <summary>
@@ -201,7 +216,18 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// </summary>
 		public static RichText Concat(params RichText[] texts)
 		{
-			throw new NotImplementedException();
+			if (texts == null || texts.Length == 0)
+				return Empty;
+			else if (texts.Length == 1)
+				return texts[0];
+			string newText = string.Concat(texts.Select(txt => txt.text));
+			RichTextModel model = texts[0].ToRichTextModel();
+			int offset = texts[0].Length;
+			for (int i = 1; i < texts.Length; i++) {
+				model.Append(offset, texts[i].stateChangeOffsets, texts[i].stateChanges);
+				offset += texts[i].Length;
+			}
+			return new RichText(newText, model);
 		}
 		
 		/// <summary>
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
index ca1f588612..7a5f604a27 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
@@ -4,6 +4,8 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
 using System.Windows;
 using System.Windows.Media;
 using ICSharpCode.NRefactory.Editor;
@@ -72,6 +74,7 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// </summary>
 		internal RichTextModel(int[] stateChangeOffsets, HighlightingColor[] stateChanges)
 		{
+			Debug.Assert(stateChangeOffsets[0] == 0);
 			this.stateChangeOffsets.AddRange(stateChangeOffsets);
 			this.stateChanges.AddRange(stateChanges);
 		}
@@ -85,9 +88,18 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		{
 			if (e == null)
 				throw new ArgumentNullException("e");
-			for (int i = 0; i < stateChangeOffsets.Count; i++) {
-				stateChangeOffsets[i] = e.GetNewOffset(stateChangeOffsets[i]);
-			}
+			UpdateOffsets(e.GetNewOffset);
+		}
+		
+		/// <summary>
+		/// Updates the start and end offsets of all segments stored in this collection.
+		/// </summary>
+		/// <param name="change">OffsetChangeMap instance describing the change to the document.</param>
+		public void UpdateOffsets(OffsetChangeMap change)
+		{
+			if (change == null)
+				throw new ArgumentNullException("change");
+			UpdateOffsets(change.GetNewOffset);
 		}
 		
 		/// <summary>
@@ -96,12 +108,52 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// <param name="change">OffsetChangeMapEntry instance describing the change to the document.</param>
 		public void UpdateOffsets(OffsetChangeMapEntry change)
 		{
-			for (int i = 0; i < stateChangeOffsets.Count; i++) {
-				stateChangeOffsets[i] = change.GetNewOffset(stateChangeOffsets[i]);
+			UpdateOffsets(change.GetNewOffset);
+		}
+		
+		void UpdateOffsets(Func<int, AnchorMovementType, int> updateOffset)
+		{
+			int readPos = 1;
+			int writePos = 1;
+			while (readPos < stateChangeOffsets.Count) {
+				Debug.Assert(writePos <= readPos);
+				int newOffset = updateOffset(stateChangeOffsets[readPos], AnchorMovementType.Default);
+				if (newOffset == stateChangeOffsets[writePos - 1]) {
+					// offset moved to same position as previous offset
+					// -> previous segment has length 0 and gets overwritten with this segment
+					stateChanges[writePos - 1] = stateChanges[readPos];
+				} else {
+					stateChangeOffsets[writePos] = newOffset;
+					stateChanges[writePos] = stateChanges[readPos];
+					writePos++;
+				}
+				readPos++;
 			}
+			// Delete all entries that were not written to
+			stateChangeOffsets.RemoveRange(writePos, stateChangeOffsets.Count - writePos);
+			stateChanges.RemoveRange(writePos, stateChanges.Count - writePos);
 		}
 		#endregion
 		
+		/// <summary>
+		/// Appends another RichTextModel after this one.
+		/// </summary>
+		internal void Append(int offset, int[] newOffsets, HighlightingColor[] newColors)
+		{
+			Debug.Assert(newOffsets.Length == newColors.Length);
+			Debug.Assert(newOffsets[0] == 0);
+			// remove everything before offset:
+			while (stateChangeOffsets.Count > 0 && stateChangeOffsets.Last() <= offset) {
+				stateChangeOffsets.RemoveAt(stateChangeOffsets.Count - 1);
+				stateChanges.RemoveAt(stateChanges.Count - 1);
+			}
+			// Append the new segments
+			for (int i = 0; i < newOffsets.Length; i++) {
+				stateChangeOffsets.Add(offset + newOffsets[i]);
+				stateChanges.Add(newColors[i]);
+			}
+		}
+		
 		/// <summary>
 		/// Gets a copy of the HighlightingColor for the specified offset.
 		/// </summary>
diff --git a/src/Main/Base/Project/Src/Gui/Pads/CompilerMessageView/CompilerMessageView.cs b/src/Main/Base/Project/Src/Gui/Pads/CompilerMessageView/CompilerMessageView.cs
index 1591db7faf..e9edf212db 100644
--- a/src/Main/Base/Project/Src/Gui/Pads/CompilerMessageView/CompilerMessageView.cs
+++ b/src/Main/Base/Project/Src/Gui/Pads/CompilerMessageView/CompilerMessageView.cs
@@ -50,7 +50,9 @@ namespace ICSharpCode.SharpDevelop.Gui
 				return this.SelectedMessageViewCategory;
 			}
 			set {
-				throw new NotImplementedException();
+				int index = messageCategories.IndexOf(value as MessageViewCategory);
+				if (index >= 0)
+					SelectedCategoryIndex = index;
 			}
 		}