Cargo Features

[dependencies]
check_keyword = { version = "0.3.1", default-features = false, features = ["2021", "2018"] }
default = 2021

The 2021 feature is set by default whenever check_keyword is added without default-features = false somewhere in the dependency tree.

2021 default = 2018
2018 2021

CheckKeyword has 3 features without comments.