27.3.7  Column-span and row-span extent
Figure 27-2
shows the range of cells that are given headers="cspan1"
or  headers="rspan2", or both, when ColSpanIDs=Yes, RowSpanIDs=Yes, ColSpanHead=cspan,
and RowSpanHead=rspan.
Figure 27-2  Extent of column and row spans
