The navigation document lacks landmark navigation for cover, toc, or bodymatter.
PreFlight audits your chapter structure and synthesizes a valid landmarks navigation block in nav.xhtml.
Landmarks tell screen readers and assistive devices where the cover, table of contents, and actual story text start, allowing readers to jump straight to Chapter 1.
Required by EPUB 3 Structural Semantics specification and WCAG 2.1 AA navigation guidelines.
Technical Specification: nav.xhtml should contain a <nav epub:type="landmarks"> with links to epub:type="bodymatter", "toc", and "cover-image".