Cargo Features

[dependencies]
async-event-emitter = { version = "0.1.3", default-features = false, features = ["use-async-std", "tokio"] }
default = tokio

The tokio feature is set by default whenever async-event-emitter is added without default-features = false somewhere in the dependency tree.

use-async-std = async-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.

async-std use-async-std?
tokio default