# Meta Attributes

Like Nix packages, NixOS modules can declare meta-attributes to provide extra information. Module meta attributes are defined in the `meta.nix` special module.

`meta` is a top level attribute like `options` and `config`. Available meta-attributes are `maintainers`, `doc`, and `buildDocsInSandbox`.

Each of the meta-attributes must be defined at most once per module file.

    { config, lib, pkgs, ... }:
    {
      options = {
        ...
      };

      config = {
        ...
      };

      meta = {
        maintainers = with lib.maintainers; [ ericsagnes ];
        doc = ./default.xml;
        buildDocsInSandbox = true;
      };
    }

- `maintainers` contains a list of the module maintainers.

- `doc` points to a valid DocBook file containing the module documentation. Its contents is automatically added to . Changes to a module documentation have to be checked to not break building the NixOS manual:

      $ nix-build nixos/release.nix -A manual.x86_64-linux

- `buildDocsInSandbox` indicates whether the option documentation for the module can be built in a derivation sandbox. This option is currently only honored for modules shipped by nixpkgs. User modules and modules taken from `NIXOS_EXTRA_MODULE_PATH` are always built outside of the sandbox, as has been the case in previous releases.

  Building NixOS option documentation in a sandbox allows caching of the built documentation, which greatly decreases the amount of time needed to evaluate a system configuration that has NixOS documentation enabled. The sandbox also restricts which attributes may be referenced by documentation attributes (such as option descriptions) to the `options` and `lib` module arguments and the `pkgs.formats` attribute of the `pkgs` argument, `config` and the rest of `pkgs` are disallowed and will cause doc build failures when used. This restriction is necessary because we cannot reproduce the full nixpkgs instantiation with configuration and overlays from a system configuration inside the sandbox. The `options` argument only includes options of modules that are also built inside the sandbox, referencing an option of a module that isn’t built in the sandbox is also forbidden.

  The default is `true` and should usually not be changed; set it to `false` only if the module requires access to `pkgs` in its documentation (e.g. because it loads information from a linked package to build an option type) or if its documentation depends on other modules that also aren’t sandboxed (e.g. by using types defined in the other module).