See W3C documentation for the XHTML table model.
An abbreviated version of the cell’s content. This allows visual browsers to use the short form if space is limited, and non-visual browsers can give a cell’s header information in an abbreviated form before rendering each cell.
This attribute was not widely supported as of December 2002.
|Text, numbers, or special characters||A brief note of what is in the cell, mostly for use by accessibility software|
|Restriction: This attribute may be specified if the element is used.|