Nix (language)
The Nix language is designed for conveniently creating and composing derivations – precise descriptions of how contents of existing files are used to derive new files.
Note: Check the Nix Reference Manual on the Nix Language for up-to-date documentation and Nix language basics for a gentle introduction.
The .nix files are written in the Nix language. While being a NixOS user doesn't demand complete mastery of Nix, customizing code snippets is necessary.