Cargo Features

intervaltree = { version = "0.2.7", default-features = false, features = ["std", "serde"] }
default = std

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

std default

Features from optional dependencies

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

serde implicit feature

With alloc and derive