Mix.SCM.accepts_options

You're seeing just the callback accepts_options, go back to Mix.SCM module for more information.
Link to this callback

accepts_options(app, opts)

View Source

Specs

accepts_options(app :: atom(), opts()) :: opts() | nil

This behaviour function receives a keyword list of opts and should return an updated list in case the SCM consumes the available options. For example, when a developer specifies a dependency:

{:foo, "0.1.0", github: "foo/bar"}

Each registered SCM will be asked if they consume this dependency, receiving [github: "foo/bar"] as argument. Since this option makes sense for the Git SCM, it will return an update list of options while other SCMs would simply return nil.