Function ranked_rows 

pub fn ranked_rows<'a, R>(
    index: &ListIndex,
    query: &str,
    rows: impl IntoIterator<Item = R>,
) -> Vec<usize>
where
    R: IntoIterator<Item = (&'a str, FieldWeight)>,

The rows of a short list that answer query, best first, ranked by index the way every list search ranks; rows that rank alike keep the list’s order, so a list does not reshuffle while a word is typed. An empty query keeps every row in order.