Definition
EPUB
EPUB is the open ebook format accepted by every major store — Amazon KDP, Apple Books, Kobo. A valid EPUB3 contains per-chapter files, a navigation table of contents, and metadata.
Under the hood an EPUB is a zip archive of XHTML chapters plus a package document and nav file. Reader apps build their chapter menus from the nav document — which is why badly converted books show one giant chapter. Amazon converts uploaded EPUBs to its internal format on ingestion, so one clean EPUB serves every store.
Related tools & guides
Authoritative sources: w3.org
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