Adapter composition: parseable leaf content grafts an inner arbor.
Part of [Quarb](https://quarb.org), a query language for *arbors*
— tree-spanned graphs. This crate is shared infrastructure for the
[`quarb`](https://crates.io/crates/quarb) engine and its adapters.
See [quarb.org](https://quarb.org) for the language specification
and the user guide.
Dual-licensed under either of [MIT](LICENSE-MIT) or
[Apache-2.0](LICENSE-APACHE), at your option.