pub fn set_keyed(&mut self, plan: &Plan<V>, keys: &[usize], handle: &KeysValsHandle<V>) {
        self.arrangements
            .entry(plan.clone())
            .or_insert(HashMap::new())
            .insert(keys.to_vec(), handle.clone());
    }
Installs a keyed arrangement for a specified plan and sequence of keys.
interactive/src/manager.rs