Evolution

Every discovered bug adds the smallest regression at the seam where it is observable. Parser upgrades rerun the positive corpus and properties. Future format adapters and renderer layers must satisfy the same semantic contract; they do not add parser-specific assertions to the mdBook protocol.

Format extensions

Future adapters for tree-shaped, JSON-compatible formats may target the existing StructuredDocument. They must preserve its ordering, scalar, provenance, and error invariants without exposing parser-specific representations. A format whose parsed values cannot be represented losslessly requires a different model or rendering layer rather than a lossy adapter.

Deferred features

JSON Pointer-generated anchors, schema-aware and domain-specific views, persistent expansion state, alternate backends, print-specific behavior, and deeper mdBook integration remain deferred. These exclusions preserve the v1 boundary until implementation evidence establishes a need to change it.

Possible mdBook contributions

Any proposed mdBook core change remains a separate generic contribution. Candidates include chapter-aware link resolution, duplicate output-path diagnostics, and an explicit UTF-8 textual-source contract.

A dependency-reporting API is considered only after a prototype establishes a reproducible mdbook serve rebuild problem. No first-class content-kind field or format-specific behavior enters mdBook core without a versioned protocol design.