procedure TMemoStrings.Insert(Index: Integer; const S: string);
var
SelStart, LineLen: Integer;
Line: string;
begin
if Index >= 0 then
begin
SelStart := SendMessage(Memo.Handle, EM_LINEINDEX, Index, 0);
if SelStart >= 0 then Line := S + #13#10 else
begin
SelStart := SendMessage(Memo.Handle, EM_LINEINDEX, Index - 1, 0);
if SelStart < 0 then Exit;
LineLen := SendMessage(Memo.Handle, EM_LINELENGTH, SelStart, 0);
if LineLen = 0 then Exit;
Inc(SelStart, LineLen);
Line := #13#10 + s;
end;
SendMessage(Memo.Handle, EM_SETSEL, SelStart, SelStart);
SendMessage(Memo.Handle, EM_REPLACESEL, 0, Longint(PChar(Line)));
end;
end;