Batten on a hobie sail kit

I was reading the directions that come with the hobie sail kit. Step 5 says to tie on the batten. But doesnt show you exactly where to tie it, or even what it does. I searched google, and couldnt come up with anything. THe deffinitions I got for batten didnt help me much either.

A batten is a stiffener. It is usually a strip of plastic that fits in a pocket sewn into the sail. From the pictures on the Hobie site, yours runs from about midway up the mast to the top outer corner of the sail.