//! Registry tree: the one `Registry` type plus the pure operations over it.
//! 注册树:唯一的 `Registry` 类型与作用于其上的纯操作。
//!
//! The file tree mirrors the module tree: `tree/tree.rs` is this module, and
//! every child is a `目录/同名.rs` file it declares with `#[path]`.
//! 文件树与模块树一致:`tree/tree.rs` 就是本模块,每个子模块都是它用 `#[path]`
//! 声明的 `目录/同名.rs`。
pub use *;