Enhancement: docker exec -container_index ...

Often times I start a new container in one terminal, then docker exec something in another terminal. I use zsh and I have the completions installed, so docker exec <TAB> lets me to select a container quickly.
However I think that accessing a container by index (i.e like cd -3 or git show HEAD~7) can also be useful and more convenient. docker exec -4 /bin/bash will refer to the fourth container in docker ps, and so on.

I thought to add it as part of the zsh Docker completion script, but perhaps it should be added in the CLI itself?

I couldn't find any existing issue requesting such a feature, hence opening a new one.

Start at the docker exec entry point and the zsh Docker completion script mentioned in the issue, then determine whether container-index handling belongs in the CLI or completion layer. Compare the requested index against docker ps ordering and define behavior for invalid or changing indexes; done means docker exec -4 resolves the intended container with coverage for the chosen layer.