There is this unofficial style guide which covers what you need: (I use it when in doubt)
GitHub - christopheradams/elixir_style_guide: A community driven style guide for Elixir · GitHub
And then Lexmag’s style guide which was the foundation for mix format IIRC.
GitHub - lexmag/elixir-style-guide: An opinionated Elixir style guide · GitHub
