Function rfr 

pub(crate) fn rfr(
    name: &str,
    currency: &str,
    day_count: DayCountFraction,
    fixing_center: &str,
    publication_lag_days: u16,
) -> OvernightIndex

Builds an overnight index, resolving its fixing calendar from a business-center code (single or comma-joined, per the lookup DSL). The business-day convention is modified-following and the end-of-month rule is off for every standard overnight (RFR) index.