anchor.diff:                      --home "$home" \
                       --shell "$shell" \
                       ''${createHome:+--create-home} \
  +                    ''${isAlias:+--non-unique} \
                       "$name"
                   if test "''${password:0:1}" = 'X'; then
                       (echo "''${password:1}"; echo "''${password:1}") | ${pkgs.shadow}/bin/passwd "$name"
  
positive.code:           then not modify any of the basic properties for the user account.
          ";
        };
        
      };
  
      config = {
  
negative.code:   users = config.users;
  
    userOpts = { name, config, ... }: {
  
      options = {
  
        name = mkOption {
          type = with types; uniq string;
          description = "The name of the user account. If undefined, the name of the attribute set will be used.";
        };
  
        description = mkOption {
          type = with types; uniq string;
          default = "";
          description = "A short description of the user account.";
        };
  
        uid = mkOption {
          type = with types; uniq (nullOr int);
          default = null;
          description = "The account UID. If undefined, NixOS will select a free UID.";
        };
  
        group = mkOption {
          type = with types; uniq string;
          default = "nogroup";
          description = "The user's primary group.";
        };
  
        extraGroups = mkOption {
          type = types.listOf types.string;
          default = [];
          description = "The user's auxiliary groups.";
        };
  
        home = mkOption {
          type = with types; uniq string;
          default = "/var/empty";
          description = "The user's home directory.";
        };
  
        shell = mkOption {
          type = with types; uniq string;
          default = "/run/current-system/sw/sbin/nologin";
          description = "The path to the user's shell.";
        };
  
        createHome = mkOption {
          type = types.bool;
          default = false;
          description = "If true, the home directory will be created automatically.";
        };
  
        useDefaultShell = mkOption {
          type = types.bool;
          default = false;
          description = "If true, the user's shell will be set to <literal>users.defaultUserShell</literal>.";
        };
  
        password = mkOption {
          type = with types; uniq (nullOr string);
          default = null;
          description = "The user's password. If undefined, no password is set for the user.  Warning: do not set confidential information here because this data would be readable by all.  This option should only be used for public account such as guest.";
        };
  
        isSystemUser = mkOption {
          type = types.bool;
          default = true;
          description = "Indicates if the user is a system user or not.";
        };
  
        createUser = mkOption {
          type = types.bool;
          default = true;
  