Function remap_layered 

pub fn remap_layered<'a, 'b, A, F>(
    source: &str,
    node_name: &str,
    namespace: &str,
    authoritative: A,
    fallback: F,
) -> Option<ResolvedName>
where
    A: IntoIterator<Item = (&'a str, &'a str)>,
    F: IntoIterator<Item = (&'b str, &'b str)>,

resolve_name_layered’s SUBSTITUTION, without its expansion: the name the first matching rule (authoritative tier first) sends source to, or None when no rule matches or source does not expand.

For a caller that has never expanded names and must not start: on None it passes source through exactly as before, so a node with no matching rule sees no change at all. NodeHandle is that caller.