As in: index slice and face arity slice.
For example, given the type
MeshBuffer<UnboundedPolygon<usize>, Vec3>, the as_index_slice function returns &[UnboundedPolygon<usize>]. Each element of that slice has an independent arity that can be queried via the DynamicArity trait's arity function.
Is that what you're looking for? :-) If so, take a look at the
MeshBufferN type definition. It's the same as the (very long) type I mentioned above, but spelled out in the much shorter form MeshBufferN<usize, Vec3>.
I'm working on a new version of my https://crates.io/crates/nsi crate and I wanted to add a sample where some plexus geometry is rendered as a subdiv surface with creases. :)