Grow this cell to *width* grid columns and *height* rows by expanding
        horizontal spans and creating continuation cells to form vertical
        spans.

def _grow_to(self, width, height, top_tc=None):
        """
        Grow this cell to *width* grid columns and *height* rows by expanding
        horizontal spans and creating continuation cells to form vertical
        spans.
        """
        def vMerge_val(top_tc):
            if top_tc is not self:
                return ST_Merge.CONTINUE
            if height == 1:
                return None
            return ST_Merge.RESTART

        top_tc = self if top_tc is None else top_tc
        self._span_to_width(width, top_tc, vMerge_val(top_tc))
        if height > 1:
            self._tc_below._grow_to(width, height-1, top_tc)