//! Packaging primitives shared by container-based document formats.
//!
//! A container format — an e-book or office-document package — is a ZIP archive of XML parts. This
//! module supplies the two pieces such a writer builds on: a deterministic [`zip`] archive builder
//! (and matching reader) and a small [`xml`] emitter that always produces well-formed output. Both
//! are byte-reproducible: identical inputs yield identical bytes.