Function from_scheme_instances_with_name 

pub fn from_scheme_instances_with_name<'a, A, I, F>(
    instances: I,
    to_arg: F,
    target_scheme_name: &str,
) -> ValueAssignment<A>
where
    A: Eq + Hash + Clone,
    I: IntoIterator<Item = (&'a SchemeInstance, &'a HashMap<String, String>)>,
    F: Fn(&SchemeInstance) -> A,

Same as from_scheme_instances but lets the caller specify a custom values-scheme name (for consumers who register their own variant).