The drawing of the cells is concern of the cells themselves and not of MarkupGrid, right?
I.e. the "MarkupGrid XML Component" that's named in MarkupGrid.itemComponentName - and then it takes care of rendering its content.
If you just put text label there, only text will be drawn. If add a bounding box, box will be drawn and so on...
(i am speaking by merely having had a glance at TFM, so correct me if wrong)