Cargo Features

der-parser = { version = "9.0.0", default-features = false, features = ["std", "bigint", "serialize", "unstable"] }
default = std

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

std default serialize?
bigint = num-bigint
serialize = cookie-factory, std

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.

num-bigint bigint?