Cargo Features

macaddr = { version = "1.0.1", default-features = false, features = ["std", "serde_std"] }
default = std

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

std default serde_std?
serde_std = std

Enables std of 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.

serde serde_std?