Remove merge from this (merge-origin) cell.

        The merged cell represented by this object will be "unmerged",
        yielding a separate unmerged cell for each grid cell previously
        spanned by this merge.

        Raises |ValueError| when this cell is not a merge-origin cell. Test
        with `.is_merge_origin` before calling.

def split(self):
        """Remove merge from this (merge-origin) cell.

        The merged cell represented by this object will be "unmerged",
        yielding a separate unmerged cell for each grid cell previously
        spanned by this merge.

        Raises |ValueError| when this cell is not a merge-origin cell. Test
        with `.is_merge_origin` before calling.
        """
        if not self.is_merge_origin:
            raise ValueError(
                'not a merge-origin cell; only a merge-origin cell can be sp'
                'lit'
            )

        tc_range = TcRange.from_merge_origin(self._tc)

        for tc in tc_range.iter_tcs():
            tc.rowSpan = tc.gridSpan = 1
            tc.hMerge = tc.vMerge = False