TAdvGridExcelExport Borders

Hello,

currently I am modifying some VCL-Apps to use the new XLSX-Format.

In the old apps I used TAdvGridExcelIO for the Export and the Event OnCellFormat:

procedure TfrmMain.AdvGridExcelIOCellFormat(Sender: TAdvStringGrid;
  const GridCol, GridRow, XlsCol, XlsRow: Integer; const Value: WideString;
  var Format: TFlxFormat);
begin
 if (GridRow = 0) then Format.Font.Style := [flsBold];
 Format.Borders.Left.Style := TFlxBorderStyle.fbs_Thin;
 Format.Borders.Right.Style := TFlxBorderStyle.fbs_Thin;
 Format.Borders.Top.Style := TFlxBorderStyle.fbs_Thin;
 Format.Borders.Bottom.Style := TFlxBorderStyle.fbs_Thin;
 Format.Font.ColorIndex := 1;
end;

We bought FlexCell and I installed the TMS GridFilters.

I cannot find any information in the documentation about exporting the Borders in the OnExportCell-Event of TAdvGridExcelExport:

procedure TfrmMain.AdvGridExcelExportExportCell(Sender: TObject;
  var Args: TExportCellEventArgs);
begin // Doesn't work
 if (Args.GridRow = 0) then Args.CellFormat.Font.Style := [TFlxFontStyles.Bold];
 Args.CellFormat.Borders.Left.Style := TFlxBorderStyle.Thin;
 Args.CellFormat.Borders.Right.Style := TFlxBorderStyle.Thin;
 Args.CellFormat.Borders.Top.Style := TFlxBorderStyle.Thin;
 Args.CellFormat.Borders.Bottom.Style := TFlxBorderStyle.Thin;
 Args.CellFormat.Font.Color.Index := 1;
end;

The above code doesn't work - left side cannot be assigned to... 
Code completion in the IDE doesn't help either.

What is the correct way to export the borders?

Thanks in advance.

Yours sincerely

Matthias