Cargo Features

[dependencies]
chacha20-poly1305 = { version = "0.1.1", default-features = false, features = ["std", "alloc"] }
default = std

The std feature is set by default whenever chacha20-poly1305 is added without default-features = false somewhere in the dependency tree.

std default = alloc
alloc std

ChaCha20Poly1305 has 3 features without comments.