Rust API Design

Everything pub from the crate root is a promise to every downstream caller. This skill governs what callers can see and rely on — the exported surface, the shape of its traits and generics, and which changes break the promise.

The surface is the contract

Default to private and export deliberately: a type pub only because a pub fn returns it is still part of the API, impls and public fields included. Make pub(crate) the habit; re-export the surface from lib.rs, module paths private:

// lib.rs
pub use crate::internal::parser::Parser; // the surface
mod internal;                            // the tree stays private