Cargo Features

[dependencies]
old-http = { version = "0.1.1-pre", default-features = false, features = ["ssl"] }
default = ssl

The ssl feature is set by default whenever old-http is added without default-features = false somewhere in the dependency tree.

ssl default = openssl

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 ssl

Enables openssl ^0.2