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.

def tblStyle_val(self, styleId):
        """
        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.
        """
        tblPr = self.tblPr
        tblPr._remove_tblStyle()
        if styleId is None:
            return
        tblPr._add_tblStyle().val = styleId