I think he's just talking about the ability to collapse something after you've read it, which is a great feature on reddit - particularly on mobile. I use it a

I think he's just talking about the ability to collapse something after you've read it, which is a great feature on reddit - particularly on mobile. I use it all the time. I read as much of the comment tree as i'm interested in, then collapse the root node to move on to the next one. It makes it easier than having to scan down and do visual indentation tracking.