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 and
  doc.
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; 
  };
}
 
  
    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