Function discourage 

const fn discourage(
    id: &'static str,
    when: &'static [Condition],
    setting: &'static str,
    avoid: &'static [Value],
    default: Value,
    basis: Basis,
    reason: &'static str,
    source: &'static str,
) -> Rule

A discouraged choice: setting should be none of avoid; default replaces it.