code: def tblStyle_val(self, styleId):
          
          tblPr = self.tblPr
          tblPr._remove_tblStyle()
          if styleId is None:
              return
          tblPr._add_tblStyle().val = styleId
docs: Set the value of `w:tblPr/w:tblStyle/@w:val` (a table style id) to
          *styleId*. If *styleId* is None, remove the `w:tblStyle` element.