ITextUndoHistory ITextUndoHistoryRegistry.RegisterHistory(object context)
        {
            IBasicUndoHistory history;

            if (!_map.TryGetValue(context, out history))
            {
                history = new BasicUndoHistory(context);
                _map.Add(context, history);
            }
            return(history);
        }
 internal BasicUndoTransaction(BasicUndoHistory textUndoHistory, string description)
 {
     _textUndoHistory = textUndoHistory;
     Description      = description;
 }