Alsing.SourceCode.SyntaxDocument.DeleteRange C# (CSharp) Метод

        public void DeleteRange(TextRange Range, bool StoreUndo)
        {
            TextRange r = Range;
            Modified = true;
            if (StoreUndo)
            {
                string deltext = GetRange(Range);
                PushUndoBlock(UndoAction.DeleteRange, deltext, r.FirstColumn, r.FirstRow);
            }


            if (r.FirstRow == r.LastRow)
            {
                Row xtr = this[r.FirstRow];
                int max = Math.Min(r.FirstColumn, xtr.Text.Length);
                string left = xtr.Text.Substring(0, max);
                string right = "";
                if (xtr.Text.Length >= r.LastColumn)
                    right = xtr.Text.Substring(r.LastColumn);
                xtr.Text = left + right;
            }
            else
            {
                if (r.LastRow > Count - 1)
                    r.LastRow = Count - 1;

                Row xtr = this[r.FirstRow];
                if (r.FirstColumn > xtr.Text.Length)
                {
                    int diff = r.FirstColumn - xtr.Text.Length;
                    var ws = new string(' ', diff);
                    InsertText(ws, xtr.Text.Length, r.FirstRow, true);
                    //return;
                }

                string row1 = xtr.Text.Substring(0, r.FirstColumn);

                Row xtr2 = this[r.LastRow];
                int Max = Math.Min(xtr2.Text.Length, r.LastColumn);
                string row2 = xtr2.Text.Substring(Max);

                string tot = row1 + row2;
                //bool fold=this[r.LastRow].IsCollapsed | this[r.FirstRow].IsCollapsed ;

                int start = r.FirstRow;
                int end = r.LastRow;

                for (int i = end - 1; i >= start; i--)
                {
                    Remove(i, false, false);
                }

                //todo: DeleteRange error						
                //this.Insert ( tot  ,r.FirstRow,false);


                Row row = this[start];
                row.Expanded = true;
                row.Text = tot;
                row.startSpans.Clear();
                row.endSpans.Clear();
                row.startSpan = null;
                row.endSpan = null;
                row.Parse();
            }

            ResetVisibleRows();
            OnChange();
        }