[rgoulter]

You can see how it's used in the GitHub actions of devenv:

It calls `devenv ci` (which checks that the devenv file is good), then runs a 'script' in the devenv file... https://github.com/cachix/devenv/blob/8bea91cd1073b0d51cf96e...

The 'script' in the devenv file: https://github.com/cachix/devenv/blob/8bea91cd1073b0d51cf96e...