Cargo Features

[dependencies]
extra-default = { version = "0.2.0", default-features = false, features = ["std", "alloc", "collections"] }
default = std

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

std default = collections
alloc collections?
collections std = alloc

extra-default has 4 features without comments.