Add the width of *other_tc* to this cell. Does nothing if either this
        tc or *other_tc* does not have a specified width.

def _add_width_of(self, other_tc):
        """
        Add the width of *other_tc* to this cell. Does nothing if either this
        tc or *other_tc* does not have a specified width.
        """
        if self.width and other_tc.width:
            self.width += other_tc.width