I think they're going for the minimal line count by in lining the docstrings. In some of my own scripts, I've lifted an idea that I saw in the wild where your Usage header and function docstrings are just prefixed with '#/', a more aesthetic and equally unlikely string (which also looks good in blocks, so it could even be restricted to newlines that just are comments, letting the line count breath a but and removing any worry of accidentally using that sequence in code). Our help function would then just 'grep w/e $BASH_SOURCE | cut w/e'.

is Docker married to btrfs?

Docker defaults to overlay2, but supports btrfs and others: https://docs.docker.com/storage/storagedriver/select-storage...

"Bocker" uses btrfs only.

I wish Docker had been kept as simple as possible. A Bocker that uses overlay2 could potentially be a Docker-like MVP.