public void ClearRedoStack()
{
if (redostack.Count != 0)
{
redostack.Clear();
NotifyPropertyChanged("CanRedo");
// if the "original file" marker is on the redo stack: remove it
if (elementsOnUndoUntilOriginalFile < 0)
elementsOnUndoUntilOriginalFile = int.MinValue;
}
}