Function reference_stated 

const fn reference_stated(
    id: &'static str,
    when: &'static [Condition],
    setting: &'static str,
    values: &'static [Value],
    reason: &'static str,
    source: &'static str,
) -> Rule

The original authors’ setting as their README or a code comment instructs it (“do X”, “we recommend X”), without saying why it is needed or better: still Kind::Reference.