EPUB 3.1 Changes from EPUB 3.0.1

Editor's Draft 26 April 2016

This document summarizes changes included in the most current draft of EPUB 3.1. Note that this list of changes is not exhaustive; additional changes are under consideration and will be included in forthcoming drafts.

Summary of Changes from Previous Editor's Draft
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Markus Gylling, International Digital Publishing Forum (IDPF)

Matt Garrish, Invited Expert

Copyright © 2010-2016 International Digital Publishing Forum™

All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and dissemination of this work with changes is prohibited except with the written permission of the International Digital Publishing Forum (IDPF).

EPUB is a registered trademark of the International Digital Publishing Forum.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document.

This document is a draft produced by the EPUB Working Group under the EPUB Working Group Charter approved on 8 July 2015.

This document is not considered stable and may be updated, replaced or obsoleted at any time. Its publication as a draft does not imply endorsement by IDPF membership or the IDPF Board. The document should only be cited as a work in progress.

Feedback on this document can be provided to the EPUB Working Group's mailing list or issue tracker.

This document is governed by the IDPF Policies and Procedures.

  1 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.

This document, EPUB 3.1 Changes from EPUB 3.0.1, describes changes made in the first major revision of the EPUB 3.0 specifications, highlighting key changes and additions.

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 [EPUB31].

  1.1 EPUB Revision History

EPUB had its roots in the interchange format known as the Open EBook Publication Structure (OEBPS). OEBPS 1.0 was approved in 1999 by the Open eBook Forum, an organization that later became the International Digital Publishing Forum (IDPF). Subsequent revisions 1.1 and 1.2 were approved by the IDPF in 2001 and 2002 respectively.

It was realized that a need existed for a format standard that could be used for delivery as well as interchange, and work began in late 2005 on a single-file container format for OEPBS, which was approved by the IDPF as the OEBPS Container Format (OCF) in 2006. Work on a 2.0 revision of OEBPS began in parallel which was approved as the renamed EPUB 2.0 in October, 2007, consisting of a triumvirate of specifications: Open Package Format (OPF), Open Publication Format (OPF) together with OCF. EPUB 2.0.1, a maintenance update to the 2.0 specification set primarily intended clarify and correct errata in the specifications, was approved in September, 2010. [OPF2] [OPS2] [OCF2]

Work on a major new 3.0 revision of the EPUB specifications began in 2010, with the goal of aligning EPUB more closely with HTML5, and in the process bringing new, native multimedia features, sophisticated CSS layout rendering and font embedding, scripted interactivity, enhanced global language support, and improved accessibility. A new specification, EPUB Media Overlays was also introduced, enabling text and audio synchronization in EPUB Publications. To better align the specification names with the standard, the Open Package Format specification was renamed EPUB Publications and the Open Publication Format specification was renamed EPUB Content Documents. The EPUB 3.0 specifications were approved in October, 2011. [Publications30] [ContentDocs30] [OCF30] [MediaOverlays30]

The EPUB 3.0.1 revision was undertaken in 2013-14. Although introducing mostly minor fixes and updates, it did see the integration of Fixed Layout Documents, which give Authors greater control over presentation when a reflowable EPUB is not suitable for the content. [Publications301] [ContentDocs301] [OCF301] [MediaOverlays301]

  2 Specification Reorganization

To simplify reading and referencing of the EPUB standard, a major reorganization of the specifications was undertaken in this revision. Foremost among the changes, a new umbrella EPUB 3.1 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. These changes were intended to remove confusion that EPUB Publications are equivalent to the Package Document. All common terminology was 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 3.1 to better reflect that it defines Renditions of content through the Package Document. The EPUB Navigation Document definition was moved from [ContentDocs301] to this specification as it is a central component of a Package and not a feature to be implemented in random EPUB Content Documents. All property definitions previously defined within this specification were moved out to the [PackageVocab].

[MediaOverlays31] also saw its embedded property definitions removed to a separate vocabulary, but was otherwise unchanged structurally.

[ContentDocs31] underwent mostly cosmetic changes outside of the removal of the EPUB Navigation Document definition. Some sections were 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.

[OCF31] similarly underwent some minor editorial and structure cleanup, but no sections were added or removed.


To comment on this change, please see Issue #640.

  3 EPUB 3.1

  3.1 Accessibility Support

EPUB 3.1 adds 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].


To comment on this change, please see Issue 704.

  3.2 New Core Media Types

EPUB 3.1 adds the WOFF 2.0 and application/font-sfnt font formats as Core Media Types.

  3.3 Clarification of Foreign Resource Fallbacks

EPUB 3.1 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.


To comment on this change, please see Issue #592.

  3.4 Removed support for EPUBCFI for linking

EPUB 3.1 removes the requirement for Reading Systems to support EPUB Canonical Fragment Identifiers [EPUBCFI] for hyperlinking (cf. the EPUB 3.0.1 EPUBCFI requirement).


To comment on this change, please see Issue #662.

  4 Packages 3.1

  4.1 Dublin Core Metadata

The first Editor's Draft of EPUB 3.1 greatly reduced the available set of Dublin Core metadata elements. After considering additional feedback about the uses for the missing elements, all of the original elements have now been restored.


To comment on this change, please see Issue #642.

  4.2 The refines attribute

The refines attribute, previously used to chain metadata statements together, is superseded in EPUB 3.1. The following attributes have been added to replace the functionality it provided to Reading Systems: opf:scheme, opf:role, opf:alt-script, opf:file-as, opf:authority and opf:term.


To comment on this change, please see Issue #642.

  4.3 Linked Metadata Records

EPUB 3.1 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 the retrieval of metadata records hosted outside the container has also been defined.


To comment on this change, please see Issues #642 and #703.

  4.4 Removal of the OPF2 meta Element

EPUB 3.1 removes the [OPF2] meta element (cf. OPF2 meta element in EPUB 3.0.1).


To comment on this change, please see Issue #642.

  4.5 Removal of the NCX

The EPUB 2 NCX file for navigation is now marked as an obsolete feature (cf. EPUB 3.0.1 NCX). Support for it will be removed in the next major revision of EPUB.


The first Editor's Draft removed the NCX entirely. Support has been returned but inclusion of an NCX will generate warnings because it has moved from superseded to obsolete.


To comment on this change, please see Issue #633.

  4.6 Removal of the guide Element

EPUB 3.1 removes the deprecated guide element (cf. EPUB 3.0.1 guide element).


To comment on this change, please see Issue #644.

  4.7 Removal of the bindings Element

EPUB 3.1 does not support the 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 [HTML5] object element's intrinsic fallback mechanism (embedded content) remains for providing a Core Media Type fallback.


To comment on this change, please see Issue #639.

  5 Content Documents 3.1

  5.1 Experimental Support for HTML Syntax Removed

The first Editor's Draft of EPUB 3.1 included support for the HTML syntax of HTML5. After considering community feedback from that draft, the EPUB Working Group decided to remove support. EPUB 3.1 will instead continue to support XHTML and SVG Content Documents, as was the case with EPUB 3.0.1.

Removal of the HTML syntax is not a reflection of a lack of desire for support in EPUB, but an acknowledgement that the EPUB 3 ecosystem is not yet stable and mature enough to handle the risks that would come with the introduction of a new type of Content Document. Issues with Reading System support and additional authoring complexity to support backwards compatibility were the primary concerns cited.

The EPUB Working Group sees support for the HTML syntax evolving two ways: 1) as part of the web-friendly format currently being developed as a separate specification in IDPF; and 2) through integration into the next major revision of EPUB (i.e., EPUB 4).

  5.2 Replacement of EPUB Style Sheets with CSS References

EPUB 3.1 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 3.1 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.


To comment on this change, please see Issue #659.

  5.3 Prioritization of Author and User Styles

EPUB 3.1 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.


To comment on this change, please see Issue #693.

  5.4 Scripting Support Clarifications

EPUB 3.1 makes the following changes to scripting support:

  • Container-constrained scripting is limited to the [HTML5] 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.


To comment on this change, please see Issue #660.

  5.5 Removal of the switch Element

EPUB 3.1 does not support the inclusion 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 alttext and altimg attributes.


To comment on this change, please see Issue #637.

  5.6 Removal of the trigger Element

EPUB 3.1 does not support the 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 [HTML5] audio and video elements.


To comment on this change, please see Issue #638.

  5.7 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.

  6 Open Container Format (OCF) 3.1

  6.1 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 the the encryption.xml schema to indicate whether a resource has been compressed and its original byte size.

  Acknowledgements and Contributors

This section is informative

EPUB has been developed by the International Digital Publishing Forum in a cooperative effort, bringing together publishers, vendors, software developers, and experts in the relevant standards.

The EPUB 3.1 specifications were prepared by the International Digital Publishing Forum’s EPUB Maintenance Working Group, operating under a charter approved by the membership in July 2015, under the leadership of:

Active members of the working group included:

IDPF Members

Invited Experts/Observers

For more detailed acknowledgements and information about contributors to each version of EPUB, refer to Acknowledgements and Contributors [EPUB3Overview].


Normative References

[ContentDocs30] EPUB Content Documents 3.0 .

[ContentDocs301] EPUB Content Documents 3.0.1 .

[ContentDocs31] EPUB Content Documents 3.1 .

[EPUB31] EPUB 3.1 .

[EPUBAccessibility] EPUB Accessibility .

[MediaOverlays30] EPUB Media Overlays 3.0 .

[MediaOverlays301] EPUB Media Overlays 3.0.1 .

[MediaOverlays31] EPUB Media Overlays 3.1 .

[Publications30] EPUB Publications 3.0 .

[Publications301] EPUB Publications 3.0.1 .

[WCAG20] Web Content Accessibility Guidelines (WCAG) 2.0 . Ben Caldwel, et al. 11 December 2008.

Informative References

[EPUB3Overview] EPUB 3.1 Overview . Garth Conboy, et al.