Using <col> to add table hierarchy

You may already have seen this, but interesting and useful; how to
usefully use the col element to recognise the dual hierarchy of tables:

"When parsing the DOM to extract embedded data and a <TD> element is
encountered, treat its corresponding <COL> element as if it were the DOM
parent of the <TR> element for that cell."
http://people.csail.mit.edu/eob/2009/05/19/a-simple-extension-for-microformat-rdfa-table-support/

Of course this description is easier to say than to implement, but the use
cases are obvious.

Steven