internal void EndAtomicUndo ()
		{
			if (atomicUndoLevel <= 0)
				throw new InvalidOperationException ("There is no atomic undo operation running.");
			atomicUndoLevel--;
			Debug.Assert (atomicUndoLevel >= 0); 
			
			if (atomicUndoLevel == 0 && currentAtomicOperation != null) {
				if (currentAtomicOperation.Operations.Count > 1) {
					undoStack.Push (currentAtomicOperation);
					OnEndUndo (new UndoOperationEventArgs (currentAtomicOperation));
				} else {
					if (currentAtomicOperation.Operations.Count > 0) {
						undoStack.Push (currentAtomicOperation.Operations [0]);
						OnEndUndo (new UndoOperationEventArgs (currentAtomicOperation.Operations [0]));
					} else {
						OnEndUndo (null);
					}
				}
				currentAtomicOperation = null;
			}
			currentAtomicUndoOperationType.Pop ();
		}

		internal void BeginAtomicUndo (OperationType operationType = OperationType.Undefined)
		{
			currentAtomicUndoOperationType.Push (operationType);
			if (atomicUndoLevel == 0) {
				if (this.syntaxMode != null && !SuppressHighlightUpdate)
					Mono.TextEditor.Highlighting.SyntaxModeService.WaitUpdate (this);
			}
			if (currentAtomicOperation == null) {
				Debug.Assert (atomicUndoLevel == 0); 
				currentAtomicOperation = new AtomicUndoOperation (operationType);
				OnBeginUndo ();
			}
			atomicUndoLevel++;
		}

		public void MergeUndoOperations (int number)
		{
			number = System.Math.Min (number, undoStack.Count);
			var atomicUndo = new AtomicUndoOperation ();
			while (number-- > 0) {
				atomicUndo.Insert (0, undoStack.Pop ());
			}
			undoStack.Push (atomicUndo);
		}

		public void StackUndoToDepth (int depth)
		{
			if (undoStack.Count == depth)
				return;
			var atomicUndo = new AtomicUndoOperation ();
			while (undoStack.Count > depth) {
				atomicUndo.Operations.Insert (0, undoStack.Pop ());
			}
			undoStack.Push (atomicUndo);
		}

		public void BeginAtomicUndo ()
		{
			if (atomicUndoLevel == 0) {
				if (this.syntaxMode != null && !SuppressHighlightUpdate)
					Mono.TextEditor.Highlighting.SyntaxModeService.WaitUpdate (this);
			}
			if (currentAtomicOperation == null) {
				Debug.Assert (atomicUndoLevel == 0); 
				currentAtomicOperation = new AtomicUndoOperation ();
				OnBeginUndo ();
			}
			atomicUndoLevel++;
		}

		internal void BeginAtomicUndo (OperationType operationType = OperationType.Undefined)
		{
			currentAtomicUndoOperationType.Push (operationType);
 			if (currentAtomicOperation == null) {
				Debug.Assert (atomicUndoLevel == 0); 
				currentAtomicOperation = new AtomicUndoOperation (operationType);
				OnBeginUndo ();
			}
			atomicUndoLevel++;
		}