Pigtail on Integral Designs Poncho/Tarp / What's it for?

[FishBone]

I just got an Integral Designs poncho tarp. It's got a 9" or so cord w/cord lock "pigtail" running vertically above the rear hem, going up toward the hood. I think it might be used to shorten the back when worn in poncho mode so it tucks under a backpack, but not sure.

Anybody familiar with this product and use of the "pigtail"? Any tips on getting the most out of this piece of equipment?

thanks.