Sustainability of Digital Formats: Planning for Library of Congress Collections

EPUB Version 3.2, published as a W3C Community Group Final Report in May 2019, was an update to EPUB 3.0.1, published in June 2014. See EPUB 3.2 Final Community Group Specification 08 May 2019.

This description focuses on changes introduced in the update. See EPUB 3.2 Changes, which covers changes since EPUB 3.0.1. The intermediate version, EPUB 3.1, was declared "defunct" in early 2019 due to lack of adoption and is not described separately on this website. As stated in EPUB Revision History, "The change of version number introduced in EPUB 3.1 meant that authors, vendors and reading system developers would have to produce, distribute and consume two versions of EPUB content, but the costs of this change outweighed the benefits of the new version." For EPUB 3.2, the definition of "deprecated" is updated and the term "superseded" is dropped. The concept of "legacy" features, intended only for backward compatibility, is added. The version attribute used in the root element of a package complying with EPUB 3.2 is "3.0" -- the same as for EPUB 3.0 and EPUB 3.0.1.

The EPUB 3.2 specification involved a major reorganization of the sub-specifications. A new umbrella EPUB specification was introduced. Conformance requirements that were formerly defined in the EPUB Publications specification were moved to the new top-level specification, as were other resources applicable to several sub-specifications, including common terminology and the list of Core Media Types. An index of key concepts and terms was added to aid navigation of the various sub-specifications. The EPUB Publications specification was renamed EPUB Packages to better reflect that it defines Renditions of content through Package Documents. The EPUB Navigation Document definition was moved from the EPUB Content Documents specification to the Packages specification as it is a central component of a Package.

A major change in EPUB 3.2 is its relationship to the core web specifications of HTML, CSS, and SVG. Rather than pointing to a particular dated version of HTML or CSS. EPUB 3.2 now officially supports the current versions of HTML, CSS, and SVG, as defined by the W3C. These versions will evolve over time, allowing EPUB to remain up-to-date with the web. Note that a May 2019 agreement between W3C and the WHATWG laid out ongoing procedures for collaborative development on a single version of the HTML specification. As of May 2020, the latest W3C Recommendation for HTML 5 (https://www.w3.org/TR/html/) redirects to https://html.spec.whatwg.org/multipage/, the HTML Living Standard.

Beyond the move of the EPUB Navigation Document definition to the EPUB Packages specification, changes to the EPUB Content Documents specification were mostly cosmetic. The EPUB Media Overlays specification had no major changes beyond the move of property definitions to an annex.

EPUB 3.2 includes a recommendation that all EPUB Publications conform to the 2017 EPUB Accessibility Specification. The accessibility specification makes recommendations for the inclusion of discovery metadata along with support for Web Content Accessibility Guidelines (WCAG) 2.0.

The following specific changes were made for EPUB 3.2:

• EPUB 3.2 adds the WOFF 2.0 and SFNT font format media types as Core Media Types. The full list of Core Media Types for EPUB 3.2 includes the Internet Media Types for: HTML Content Documents that use the XHTML syntax; SVG Content Documents; CSS Style Sheets.; GIF; JPEG (JFIF); PNG; MP3 audio; AAC LC audio using MP4 container (AAC_MP4_LC); font formats -- TrueType, OpenType, WOFF, WOFF2; JavaScript; the legacy NCX navigation format; EPUB Media Overlay documents; Text-to-Speech (TTS) Pronunciation lexicons.
• EPUB 3.2 adds an additional clarification that foreign resources (i.e., resources of types not considered as Core Media Types) do not require fallbacks if they are not in the spine and not embedded in EPUB Content Documents.
• EPUB 3.2 allows fonts and resources used by scripts to be hosted outside the EPUB Container.
• EPUB 3.2 removes the requirement for Reading Systems to support EPUB Canonical Fragment Identifiers [EPUB-CFI] for hyperlinking.
• EPUB 3.2 makes some changes to package metadata. Several of these changes relate to bibliographic metadata.
  • Specialized metadata record relationships for link element are now deprecated (marc21xml-record, mods-record, onix-record, and xmp-signature). Use of the general record relationship is now preferred.
  • EPUB 3.2 also changes the precedence order of linked records, prioritizing bibliographic information in linked records over the information included directly in the Package Document metadata element.
• EPUB 3.2 removes the EPUB Style Sheets profile. In its place, more general CSS support requirements are defined.
• EPUB 3.2 makes changes related to support for scripting for more compatibility with HTML.
• EPUB 3.2 introduces a new compression element to the encryption.xml schema in the Open Container Format (OCF) specification and clarifies the order to be followed for encryption and compression.

Open specification, publicly documented. Developed under the auspices of the W3C EPUB 3 Community Group.

EPUB 3.2 was published in May 2019 by W3C as a Final Community Group Specification.

See EPUB_3_0 and EPUB_family.

See EPUB_family.

• Audio resources MAY be located outside the EPUB Container.
• Video resources MAY be located outside the EPUB Container.
• Resources retrieved by scripts MAY be located outside the EPUB Container.
• Font resources MAY be located outside the EPUB Container.

• The bytes “PK” will be at the beginning of the file, followed by two additional bytes from the ZIP specification: \003 \004
• The bytes “mimetype” will be at position 30
• actual MIME type (i.e., the ASCII string “application/epub+zip”) will begin at position 38

For early history of the EPUB format, see EPUB Revision History. The first version of EPUB 3 (EPUB_3_0) was published in 2011. EPUB 3.0.1, published in June 2014, was a minor maintenance update to EPUB 3.0.

EPUB 3.1 was published in 2017. However, in early 2019, EPUB 3.1 was declared defunct because of lack of adoption due to incompatibility with the earlier releases of EPUB 3. See introduction to EPUB 3.1 on IDPF website.

At the end of January 2017, the World Wide Web Consortium (W3C) and the International Digital Publishing Forum (IDPF) combined organizations. See IDPF News as of January 31, 2017 and New Roadmap for Future of Publishing is Underway as W3C and IDPF Officially Combine from Publishing@W3C on February 1, 2017. Development of EPUB continued under the auspices of the W3C EPUB Community Group. EPUB 3.2 was published in May 2019 by W3C as a Final Community Group Specification.