clearing a polygrid/polylist

[Mike Kerner]

How do you clear a polylist/polygrid?
set the tsvdata of widget 1 to empty # throws an error

-- 
On the first day, God created the heavens and the Earth
On the second day, God created the oceans.
On the third day, God put the animals on hold for a few hours,
   and did a little diving.
And God said, "This is good."