Cargo Features

[dependencies]
num_x = { version = "0.2.2", default-features = false, features = ["std", "num", "use_serde"] }
default = std

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

std default
num = num-traits
use_serde = serde

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.

num-traits num?
serde use_serde?