'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.'

def _span_to_width(self, grid_width, top_tc, vMerge):

    self._move_content_to(top_tc)
    while (self.grid_span < grid_width):
        self._swallow_next_tc(grid_width, top_tc)
    self.vMerge = vMerge
