I don't think my reptile guess is even correct! Oddly, my thread doesn't like doing lock chains. I have to dangle the shuttle a lot more often than normal.
I've undertaken to sew the curtains for a friend's cottage - nine windows, 18 curtains! Marietje delivered 24 metres of material, which is not going to be enough for the whole job. Unless I've misunderstood the instructions. It's not easy working from someone else's measurements. I've made two curtains and will deliver those and check that I'm on the right track before I continue. They're tab top curtains. I worked out mentally how to sew them, then consulted Pinterest to make sure. I found this tutorial. There were details like having the seam of the tab on the inside that were useful.
The facing at the top keeps the back neat. Here's back and front: