It'd be nice if `urn::Urn` implemented: - ~[`Deref<Target = str>`](https://doc.rust-lang.org/std/ops/trait.Deref.html)~ - [`PartialOrd`](https://doc.rust-lang.org/std/cmp/trait.PartialOrd.html) - [`Ord`](https://doc.rust-lang.org/std/cmp/trait.Ord.html) so that it can be used as keys in a [`BTreeMap`](https://doc.rust-lang.org/std/collections/struct.BTreeMap.html) _edit:_ ah, `Urn` already implements `Deref`.