Comment by trealira

I also just learned about it. I found this explanation of what it is: https://drup.github.io/2016/08/02/difflists/

It's a slightly confusing name, though; it makes me think of a difference list, which seems to be a completely unrelated data structure (basically a rope).

http://h2.jaguarpaw.co.uk/posts/demystifying-dlist/