[NTG-context] Setting options for every n-th row in natural TABLEs

Hi, On Edward Tufte's website, there is a discussion on zebra coloring in tables[1]. One of the suggestion is to add a horizontal rule after every third line or shade three lines with one background color and the remaining three with another background color. Is there an easy way to do this with natural TABLEs? I can do something like: \setupTABLE[row][1,2,3][background=color, backgroundcolor=gray] \setupTABLE[row][7,8,9][background=color, backgroundcolor=gray] but it requires knowing the number of lines in advance. Aditya [1]: http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0001IV