> ...which allows selecting different distributions, including Arch Linux?

Sorry to rain on your parade, but there is _no_ official Arch Linux image on Docker[1], as you can easily verify[2]. Use at your own risk whatever Arch Linux image you happen to find on Docker Hub, such as this one[3]. It might work or it might break, but it ain't official.

[1]: https://bbs.archlinux.org/viewtopic.php?id=214973

[2]: https://hub.docker.com/explore/

[3]: https://hub.docker.com/r/base/archlinux/

The attitude here is hard to understand. [3] is very clear about how it's built, no guess work involved.

Looks like heavy WIP (https://github.com/turbo/alwsl/issues/5). There isn't really anything on the main branch, indicating that it probably shouldn't be used(?) yet(?). Also, this seems to be the backstory: https://github.com/Microsoft/BashOnWindows/issues/8#issuecom...

https://github.com/turbo/alwsl/blob/master/alwsl.bat#L307 - it's a squashfs filesystem which is unpacked to replace the Ubuntu filesystem that WSL uses by default.

I was curious how the squashfs was generated too but didn't find anything describing it.

Typical of windows ecosystem and developers to sow confusion and infringe upon trademarks. Windows/Microsoft - where "X actually means Y" and always changes meaning, never for the freedom of the user, always to maintain tight control and power over computing.