Unclear at what level you're asking, but Mitchell's comment identified it as a nix-darwin feature, and you can see how he's using it in the config he linked at

Unclear at what level you're asking, but Mitchell's comment identified it as a nix-darwin feature, and you can see how he's using it in the config he linked at https://github.com/mitchellh/nixos-config/blob/b73a16fc918c501d0c00ff8f4a275fe8e83a1997/users/mitchellh/darwin.nix#L8-L25 https://github.com/mitchellh/nixos-config/blob/b73a16fc918c5...