It hangs from the clothesline by a heavy wire yoke, and you can slide it back and forth as you hang your laundry or take it off the line.
It is a handy place to keep the clothespins. When your clothes are dry, you can just drop your clothespins in.
All the clothespins are inside, ready for you when you need them.
That's why I like the clothespin bag.
This one is getting a little worn, it's getting to be time to rebuild it. Forunately, I have a plan for that.