draft of summary change proposal

Here is a draft of a rewritten table section to deal with summary.  It's still fairly rough.

This is an attempt to make more information available to assistive tech from the markup, so that less is required in summary.  I would particularly like feedback on the approach, and on ways that this goal can be achieved.

It reduces the scope of what summary is to be used for, by including

1)      An orientation attribute on the table element.  This can be used to AT to describe the reading direction of the table.

2)      Methods on the cell API to get collections of headers and headergroups

cell . cellColumnHeaders
Returns an HTMLCollection of column headers associated with this cell.
cell . cellColumnGroupHeaders
Returns an HTMLCollection of column group headers associated with this cell.
cell . cellRowHeaders
Returns an HTMLCollection of row headers associated with this cell.
cell . cellRowGroupHeaders
Returns an HTMLCollection of row group headers associated with this cell.

QUESTION:  are there implied row groups and col groups based on rowspan and colspan on th?  Should there be?

It describes what user agents, both visual and non-visual should do with summary.

It also includes an example table, based one from Wendy Chisholm.  I changed it a little, and would like feedback on that as well.

I still need to write guidance for validators, but wanted to see if this approach works for people before going any farther.