docs: def _span_to_width(self, grid_width, top_tc, vMerge):
          """
          Incorporate and then remove `w:tc` elements to the right of this one
          until this cell spans *grid_width*. Raises |ValueError| if
          *grid_width* cannot be exactly achieved, such as when a merged cell
          would drive the span width greater than *grid_width* or if not enough
          grid columns are available to make this cell that wide. All content
          from incorporated cells is appended to *top_tc*. The val attribute of
          the vMerge element on the single remaining cell is set to *vMerge*.
          If *vMerge* is |None|, the vMerge element is removed if present.
          """
          self._move_content_to(top_tc)
          while self.grid_span < grid_width:
              self._swallow_next_tc(grid_width, top_tc)
          self.vMerge = vMerge