final String[] rgs = ptm.getRowGroupSpec().split(" ");
final TableRow tr = headerGroup.newTableRow();
for (int i=0; i < rgs.length; i++) {
final PropertyDescriptor pd = (PropertyDescriptor)propertyDescriptorsMap.get(rgs[i]);
final TableHeaderCell thc = tr.newTableHeaderCell();
final MenuBar colMenu = new MenuBar(true);
if (pd instanceof SortablePropertyDescriptor) {
final MenuItem sortItem = createSortMenu((SortablePropertyDescriptor)pd);
colMenu.addItem(sortItem);