···1212configuration options.
1313:::
14141515+::: {.note}
1616+Alternatively, many packages come with extensions one might add.
1717+Examples include:
1818+- [`passExtensions.pass-otp`](https://search.nixos.org/packages/query=passExtensions.pass-otp)
1919+- [`python310Packages.requests`](https://search.nixos.org/packages/query=python310Packages.requests)
2020+2121+You can use them like this:
2222+```nix
2323+environment.systemPackages = with pkgs; [
2424+ sl
2525+ (pass.withExtensions (subpkgs: with subpkgs; [
2626+ pass-audit
2727+ pass-otp
2828+ pass-genphrase
2929+ ]))
3030+ (python3.withPackages (subpkgs: with subpkgs; [
3131+ requests
3232+ ]))
3333+ cowsay
3434+];
3535+```
3636+:::
3737+1538Apart from high-level options, it's possible to tweak a package in
1639almost arbitrary ways, such as changing or disabling dependencies of a
1740package. For instance, the Emacs package in Nixpkgs by default has a