How to add undo source code to my AddLinesMar

[jason huang]

How to add undo source code to my AddLinesMark Procedure; thanks

I don't know how to use undolist

procedure TSynEditExt.AddLinesMark;
var
  i:integer;
begin
  beginupdate;
    for I:=BlockBegin.Line-1 to BlockEnd.Line-1 do
    begin
      self.Lines[i]:='//'+self.Lines[i];
    end;
  endupdate;
end;