First, I do not believe it is possible to set the ids on the td’s or tr’s in displaytag without modifying the source. This has not left my list of things to do, but for now I have a work around for you.
Instead of defining your table:
id='row' name="..." export="true" requestURI="">
property="usefulData" title="Useful data" sortable="true" />
... more columns ...
do this:
id='row' name="..." export="true" requestURI="">
title="Useful data" sortable="true" >
id='${row.usefulData}' class='css_class_selector'>${row.usefulData}
Note the span wrapping the printed data. Now you can select the data relating printing inside your table, which is probably what you want; to select your data, as opposed to specifically selecting the td’s and tr’s.
out of my memory 