scope attribute on <entry> from proposal 62

I'm working on fixing attribute tables and encountered this new definition for @scope on <entry>:

The scope attribute can contain one of "row" or "col" or "rowgroup" or "colgroup".

scope="row"Applies to the row.

scope="col"Applies to the column.

scope="rowgroup"Applies to the row group.

scope="colgroup"Applies to the column group.

Scott (or somebody else) - can you clarify what this means? From this I really only know what values are legal, but I don't know what it means. 

Does the use of this attribute imply that the entry is a header, or is this attribute only valid when the entry is already identifiable as a header?

Also, can you clarify what a "row group" or "column group" are? My best guess is that a row group would be all rows covered by the current entry, if the entry spans rows - but I need to confirm that before it goes into the specification.

Thanks,

Robert D Anderson

IBM Authoring Tools Development

Chief Architect, DITA Open Toolkit (http://dita-ot.sourceforge.net/)