Cargo Features

rlp = { version = "0.5.2", default-features = false, features = ["std", "derive"] }
default = std

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

std default

Enables std of bytes and rustc-hex

derive = rlp-derive

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features.

rlp-derive derive?