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# Meta Attributes {#sec-meta-attributes}
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Like Nix packages, NixOS modules can declare meta-attributes to provide
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extra information. Module meta attributes are defined in the `meta.nix`
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special module.
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`meta` is a top level attribute like `options` and `config`. Available
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meta-attributes are `maintainers`, `doc`, and `buildDocsInSandbox`.
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Each of the meta-attributes must be defined at most once per module
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file.
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```nix
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{ config, lib, pkgs, ... }:
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{
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options = {
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...
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};
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config = {
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...
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};
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meta = {
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maintainers = with lib.maintainers; [ ericsagnes ];
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doc = ./default.xml;
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buildDocsInSandbox = true;
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};
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}
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```
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- `maintainers` contains a list of the module maintainers.
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- `doc` points to a valid DocBook file containing the module
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documentation. Its contents is automatically added to
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[](#ch-configuration). Changes to a module documentation have to
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be checked to not break building the NixOS manual:
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```ShellSession
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$ nix-build nixos/release.nix -A manual.x86_64-linux
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```
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- `buildDocsInSandbox` indicates whether the option documentation for the
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module can be built in a derivation sandbox. This option is currently only
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honored for modules shipped by nixpkgs. User modules and modules taken from
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`NIXOS_EXTRA_MODULE_PATH` are always built outside of the sandbox, as has
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been the case in previous releases.
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Building NixOS option documentation in a sandbox allows caching of the built
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documentation, which greatly decreases the amount of time needed to evaluate
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a system configuration that has NixOS documentation enabled. The sandbox also
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restricts which attributes may be referenced by documentation attributes
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(such as option descriptions) to the `options` and `lib` module arguments and
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the `pkgs.formats` attribute of the `pkgs` argument, `config` and the rest of
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`pkgs` are disallowed and will cause doc build failures when used. This
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restriction is necessary because we cannot reproduce the full nixpkgs
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instantiation with configuration and overlays from a system configuration
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inside the sandbox. The `options` argument only includes options of modules
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that are also built inside the sandbox, referencing an option of a module
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that isn't built in the sandbox is also forbidden.
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The default is `true` and should usually not be changed; set it to `false`
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only if the module requires access to `pkgs` in its documentation (e.g.
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because it loads information from a linked package to build an option type)
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or if its documentation depends on other modules that also aren't sandboxed
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(e.g. by using types defined in the other module).
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