Cargo Features

[dependencies]
a2 = { version = "0.10.0", default-features = false, features = ["tracing", "ring", "openssl"] }
default = openssl

The openssl feature is set by default whenever a2 is added without default-features = false somewhere in the dependency tree.

tracing

Enables tracing

ring = pem

Enables ring

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.

openssl default
pem ring?