I had been looking for vim's g<C-a> for a while and thought it didn't exist in helix until I looked up the issue tracker and found #3910.

At the bottom it appears this has been documented, and I guess this is the part that documents it:

# Selection indices (first selection is 1, second is 2, etc.)

in Special registers, but I think this is not terribly explicit (at least I don't think I would have figured out the purpose of this register with that alone). It looks like this sentence has been taken from kakoune's docs as is, but maybe the helix docs could mention "multiple selection increment" as a use case? Or maybe this belongs somewhere else which should mention this register. I have to admit I don't know what other use cases this register has!

The cherry on top would be to even have a demo like in Surround 😄
@sudormrfbin I saw that you are the one who added the demo for surround, did you use asciinema for that or something else? I know how to make a terminal cast but I don't know how you added the key strokes as you type them.