internal static void ClearSelected(TextSource ts)
        {
            var tb = ts.CurrentTB;

            Place start    = tb.Selection.Start;
            Place end      = tb.Selection.End;
            int   fromLine = Math.Min(end.iLine, start.iLine);
            int   toLine   = Math.Max(end.iLine, start.iLine);
            int   fromChar = tb.Selection.FromX;
            int   toChar   = tb.Selection.ToX;

            if (fromLine < 0)
            {
                return;
            }

            //
            if (fromLine == toLine)
            {
                ts[fromLine].RemoveRange(fromChar, toChar - fromChar);
            }
            else
            {
                ts[fromLine].RemoveRange(fromChar, ts[fromLine].Count - fromChar);
                ts[toLine].RemoveRange(0, toChar);
                ts.RemoveLine(fromLine + 1, toLine - fromLine - 1);
                InsertCharCommand.MergeLines(fromLine, ts);
            }

            //
            tb.Selection.Start = new Place(fromChar, fromLine);
            //
            ts.NeedRecalc(new TextSource.TextChangedEventArgs(fromLine, toLine));
        }
        /// <summary>
        /// Undo operation
        /// </summary>
        public override void Undo()
        {
            var tb = ts.CurrentTB;

            ts.OnTextChanging();

            tb.Selection.BeginUpdate();
            //tb.BeginUpdate();
            for (int i = 0; i < iLines.Count; i++)
            {
                int iLine = iLines[i];

                if (iLine < ts.Count)
                {
                    tb.Selection.Start = new Place(0, iLine);
                }
                else
                {
                    tb.Selection.Start = new Place(ts[ts.Count - 1].Count, ts.Count - 1);
                }

                InsertCharCommand.InsertLine(ts);
                tb.Selection.Start = new Place(0, iLine);
                string text = prevText[prevText.Count - i - 1];
                InsertTextCommand.InsertText(text, ts);
                ts[iLine].IsChanged = true;
                if (iLine < ts.Count - 1)
                {
                    ts[iLine + 1].IsChanged = true;
                }
                else
                {
                    ts[iLine - 1].IsChanged = true;
                }

                if (text.Trim() != string.Empty)
                {
                    ts.OnTextChanged(iLine, iLine);
                }
            }

            //tb.EndUpdate();
            tb.Selection.EndUpdate();

            ts.NeedRecalc(new TextSource.TextChangedEventArgs(0, 1));
        }
        internal static void InsertText(string insertedText, TextSource ts)
        {
            var tb = ts.CurrentTB;

            try {
                tb.Selection.BeginUpdate();
                char cc = '\x0';
                if (ts.Count == 0)
                {
                    InsertCharCommand.InsertLine(ts);
                }

                tb.ExpandBlock(tb.Selection.Start.iLine);
                foreach (char c in insertedText)
                {
                    InsertCharCommand.InsertChar(c, ref cc, ts);
                }

                ts.NeedRecalc(new TextSource.TextChangedEventArgs(0, 1));
            } finally {
                tb.Selection.EndUpdate();
            }
        }