Cargo Features

fritz_guess = { version = "0.1.0", default-features = false, features = ["rayon"] }
default = rayon

The rayon feature is set by default whenever fritz_guess is added without default-features = false somewhere in the dependency tree.

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

rayon default