This library provides a reader for configuration files, looking for them in places designated by (1) a user-set environment variable, (2) in the standard XDG locations (e.g., /etc/xdg/app.yml), or (3) in the classical UNIX locations (e.g. /etc/app/config.yml or ~/.apprc). Config files can be written in one of YAML, TOML, INI-style, or JSON. It enforces precedence of user-configs over system-level configs, and enviroment or command-line configs over the file-based configs.