XML format

EPUB package

The spine of an EPUB: every resource in the book, the order they are read in, and the Dublin Core metadata a shop displays.

An EPUB is a zip, and the .opf package document is what makes it a book rather than a folder of HTML. It has three parts that do different jobs: <metadata> carries the Dublin Core record a retailer displays, <manifest> lists every resource in the container, and <spine> puts the readable ones in reading order.

Manifest and spine are easy to conflate and must not be. A file that is in the manifest but not the spine — a stylesheet, an image, a cover — is part of the book but not part of the reading order. A file in neither is invisible to the reader, and a file in the spine but not the manifest makes the EPUB invalid.

Constraints that bite

Every resource in the container must appear in the manifest, and every manifest item must exist. Both directions are checked by epubcheck.
Spine itemrefs reference manifest item IDs, not file paths.
dc:identifier must match the unique-identifier attribute on the package element, or the book has no stable identity.
EPUB 3 requires a nav document with properties="nav"; the EPUB 2 NCX is optional and kept only for backwards compatibility.
The href values are relative to the .opf file's own location, not to the zip root, and the .opf is usually not at the root.

Root element: <package>
Media type: application/oebps-package+xml
Extensions: .opf
Namespaces: http://www.idpf.org/2007/opf
XMLDir label: —

Specification: EPUB 3.3 package document

A minimal valid document

Every example on this site is checked against the same parser the workspace uses, so what you see below is known to be well-formed.

epub-opf.xml

<?xml version="1.0" encoding="UTF-8"?>
<package xmlns="http://www.idpf.org/2007/opf" version="3.0" unique-identifier="pub-id">
  <metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
    <dc:identifier id="pub-id">urn:isbn:9780000000001</dc:identifier>
    <dc:title>Notes on the Analytical Engine</dc:title>
    <dc:language>en</dc:language>
    <meta property="dcterms:modified">2026-01-01T00:00:00Z</meta>
  </metadata>
  <manifest>
    <item id="nav" href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
    <item id="ch1" href="ch1.xhtml" media-type="application/xhtml+xml"/>
    <item id="css" href="style.css" media-type="text/css"/>
  </manifest>
  <spine>
    <itemref idref="ch1"/>
  </spine>
</package>

Validate your own EPUB package Extract its XPath map