27.3.1 Choosing an id/headers level

If you decide to use the id/headers method, you can choose from three levels:

Groups:	Identify column-header cells or row-header cells that apply to a block of cells, including other header cells; add headers attributes to all affected cells, identifying each by the header cell of its block.
Spans:	Identify column-header or row-header cells that explicitly or implicitly apply to multiple columns or rows of body cells; add headers attributes to all affected body cells, identifying each by the header cells that apply.
Cells:	Identify each column-header cell and row-header cell; add headers attributes to all body cells, identifying each by row and column.

First see if you can use groups to adequately identify cells; if grouping header cells does not give you enough resolution, consider span attributes; if span attributes do not suffice, use row and column IDs to provide the maximum amount of identification for each cell.

If you need to identify cells by virtual or conceptual properties, or by disjoint groupings of header cells, you might want to apply the axis attribute also, using one of the table markup methods described in §26.2.3 Assigning table-cell attribute values with dedicated formats or §26.2.4 Assigning table-cell attribute values with custom markers.

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