This document describes changes made in the second minor revision of the EPUB® 3 specifications, highlighting key changes and additions.

Introduction

EPUB is an interchange and delivery format for digital publications, based on XML and Web Standards. An EPUB Publication can be thought of as a reliable packaging of Web content that represents a digital book, magazine, or other type of publication, and that can be distributed for online and offline consumption.

EPUB 3.2 is a minor revision of the EPUB 3 specification, which can be considered as a successor to both EPUB 3.0.1 and EPUB 3.1. EPUB 3.1 did not receive wide adoption, and the Community Group decided to create EPUB 3.2 to be strongly backward-compatible with EPUB 3.0.1, while retaining many of the changes made in EPUB 3.1 (A given version of EPUB is said to be strongly backwards-compatible with an older version if and only if any EPUB publication conformant to the older version is also conformant to the newer version). All valid EPUB 3.0.1 files will also be valid EPUB 3.2 files.

This document describes all changes to EPUB made since EPUB 3.0.1, so that readers do not have to review EPUB 3.1 before being able to determine how this new version updates EPUB 3.0.1.

This document is non-normative. Consult the EPUB specifications for definitive information on EPUB 3.

Unless otherwise specified, terms used herein have the meaning defined in Terminology [[EPUB32]].

Overview

Since all valid EPUB 3.0.1 files will also be valid EPUB 3.2 files, creators of EPUB 3 publications today should not need to change anything. EPUB 3.2 does provide a few more options, and formally recommends that content creators follow the EPUB Accessibility Guidelines.

The biggest change in EPUB 3.2 is the relationship to the core web specs of HTML, CSS, and SVG. In the past EPUB has pointed 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.

Another noticeable change is that WOFF 2.0 and SFNT fonts are now Core Media Type Resources. EPUB 3.2 also deprecates some older features, such as bindings, epub:trigger, and epub:switch.

Specification Reorganization

To simplify reading and referencing of the EPUB standard, a major reorganization of the specifications was undertaken. Foremost among the changes, a new umbrella EPUB specification was introduced as the primary point of entry. EPUB Publication and Reading System requirements that were formerly defined in [[Publications301]] were moved to this new top-level specification, as was the section on Publication Resources. All common terminology were collected into this top-level specification, as well, to provide a common point of reference. An index of key concepts and terms was also added to aid navigation of the various sub-specifications.

[[Publications301]] was renamed to EPUB Packages 3.2 [[Packages32]] to better reflect that it defines Renditions of content through the Package Document. The EPUB Navigation Document definition was moved from [[ContentDocs301]] to the Packages specification as it is a central component of a Package and not a general feature of EPUB Content Documents. Property definitions previously defined within this specification were moved out to external vocabularies.

[[MediaOverlays32]] also has its embedded property definitions moved to a separate vocabulary, but is otherwise unchanged structurally.

[[ContentDocs32]] underwent mostly cosmetic changes outside of the removal of the EPUB Navigation Document definition. Some sections are renamed to better reflect that they are not unique document types but ways of enhancing content documents (e.g., the section "Scripted Content Documents" was changed to "Scripting"), but otherwise the arrangement of sections remains largely unchanged.

[[OCF32]] similarly underwent some minor editorial and structural cleanup, but no sections were added or removed.

EPUB 3.2

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the EPUB 3.0.1 specification addressed in EPUB 3.2.

Accessibility Support

EPUB 3.2 includes a recommendation that all EPUB Publications conform to the new EPUB Accessibility Specification [[EPUBAccessibility]]. The accessibility specification makes recommendations for the inclusion of discovery metadata along with [[WCAG20]] support in content.

EPUB Reading Systems are also recommended to meet the requirements in [[EPUBAccessibility]].

New Core Media Type Resources

EPUB 3.2 adds the WOFF 2.0 and SFNT font formats as Core Media Type Resources [[EPUB32]].

Clarification of Foreign Resource Fallbacks

EPUB 3.2 adds an additional clarification that foreign resources do not require fallbacks if they are not in the spine and not embedded in EPUB Content Documents.

This change will allow authors to include data files for use by scripts without unnecessary fallbacks, among other benefits.

Remotely-Hosted Resources

EPUB 3.2 allows fonts and resources used by scripts to be hosted outside the EPUB Container.

Removed support for EPUBCFI for linking

EPUB 3.2 removes the requirement for Reading Systems to support EPUB Canonical Fragment Identifiers [[EPUB-CFI]] for hyperlinking (cf. the EPUB 3.0.1 EPUBCFI requirement).

New Designations for Unsupported Features

EPUB 3.2 updates the definition of deprecated, removes “superseded,” and adds the concept of “legacy” features, intended only for backward compatibility.

Packages 3.2

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the EPUB Packages specification addressed in the 3.2 revision

Package Metadata Changes

EPUB 3.2 makes the following changes to package metadata:

Linked Metadata Records

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.

A protocol for retrieving remote records was under development in an appendix in the last draft. That work has been removed and will be continued in a separate document.

Deprecation of the bindings Element

EPUB 3.2 deprecated use of bindings in the Package Document to provide an alternative scripted fallback for foreign resources embedded in an object element (cf. EPUB 3.0.1 bindings).

The [[HTML]] object element's intrinsic fallback mechanism (embedded content) can be used to provide a fallback Core Media Type Resource.

Content Documents 3.2

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the EPUB Content Documents specification addressed in the 3.2 revision

Undated References to HTML and SVG

EPUB 3.0.1 used dated reference to HTML 5.0 and SVG 1.1, which tied the specification to those specific versions. Under this model, a new revision was required each time a version of HTML or SVG was introduced.

To ensure that that EPUB 3.2 remains up to date with the latest recommended versions of these specifications, the dated references have been replaced with undated references in EPUB 3.2. This change means that as new recommended versions of HTML and SVG are published, they are immediately valid for use in EPUB Publications.

For more information, see Relationship to HTML and Relationship to SVG.

Replacement of EPUB Style Sheets with CSS References

EPUB 3.2 removes the EPUB Style Sheets profile. In its place, more general CSS support requirements are being defined:

  • CSS support is now required for visual Reading Systems.

  • Rather than a CSS profile, EPUB 3.2 uses the “official definition” of CSS from the CSS Working Group Snapshot.

  • The restriction on the use of position: fixed is removed.

  • The restriction on the use of position: absolute is removed.

  • All -epub- prefixed properties from CSS Speech are removed due to lack of implementations.

  • The -epub-ruby-position property is removed.

  • The -epub-text-combine-horizontal property is removed.

  • The -epub-fullsize-kana property is removed.

  • The -epub-text-emphasis shorthand property is removed.

  • The use-glyph-orientation and sideways-left values of -epub-text-orientation are removed.

Prioritization of Author and User Styles

EPUB 3.2 adds guidance that Reading Systems should prioritize the style choices of Authors and users over its own user agent styles through the addition of Reading System conformance requirements and a subsection on overriding styles.

Alternate Style Tags Removed

EPUB 3.2 no longer mentions Alternate Style Tags. As this mechanism uses class attributes, this has no impact on the validity of existing content.

Any value for epub:type allowed

EPUB 3.2 allows unprefixed values that are not part of the EPUB Structural Semantics Vocabulary [[EPUB-SSV]] to be used in the epub:type attribute.

Scripting Support Clarifications

EPUB 3.2 makes the following changes to scripting support:

  • Container-constrained scripting is limited to the [[HTML]] iframe element (removed embed and object).

  • Reading Systems should support container-constrained scripting (down from "must" because of security and privacy concerns around scripting)

  • Reading Systems should support spine-level scripting in fixed layout documents and the "scrolled-doc" and "scrolled-continuous" interfaces defined by the rendition:flow property

  • If a Reading System supports spine-level scripting in reflowable documents, it must support the "scrolled-doc" interface and should support the "scrolled-continuous" interface.

Deprecation of the switch Element

EPUB 3.2 deprecates use of the switch element for conditional display of content (cf. EPUB 3.0.1 switch element).

Authors are instead directed to the existing guidance on the use of the MathML altimg attribute.

Deprecation of the trigger Element

EPUB 3.2 deprecates inclusion of the trigger element for declarative control of audio and video content (cf. EPUB 3.0.1 trigger element).

Authors are advised to use the native controls provided by the [[HTML]] audio and video elements.

epubReadingSystem Object Clarifications

An IDL definition was added for the epubReadingSystem object.

The requirements for making the object available in the different scripting contexts, including in nested contexts, were also clarified.

Open Container Format (OCF) 3.2

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the OCF specification addressed in the 3.2 revision.

Encryption

The order of encryption and compression has been clarified. The new rules clarify that compression is not necessary when it is not beneficial to reducing the size of a resource. A new Compression element has been added to the encryption.xml schema to indicate whether a resource has been compressed and its original byte size.

Media Overlays

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the Media Overlays specification addressed in the 3.2 revision.

Removal of duration attribute

Removes the duration attribute, which was added in 3.1 due to the deprecation of @refines. But since 3.2 restores @refines, and 3.1 was never implemented, duration is not needed.

EPUB Accessibility

The EPUB 3.2 revision introduces the [[EPUBAccessibility]] specification, which details how to make EPUB Publications accessible and discoverable. This specification leverages the work of [[WCAG20]] and also adds requirements for EPUB Publications. It is accompanied by the informative [[EPUBAccessibilityTechniques]] document that describes best practices for meeting the requirements.

This specification is designed to be applicable to older versions of EPUB. It can be used immediately by Authors to check whether their EPUB 3.0.1 or 2.0.1 Publications are accessible.

EPUB Canonical Fragment Identifiers

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the EPUB Canonical Fragment Identifiers specification addressed since EPUB 3.0.1.

Alternate Style Tags

The Alternate Style Tags specification is no longer referenced from EPUB 3.2.