EPUB 3.1 Changes from EPUB 3.0.1

Informational Document 5 January 2017

This version
Latest version
Previous version
Document history


Markus Gylling, International Digital Publishing Forum (IDPF)

Matt Garrish, Invited Expert

Copyright © 2010-2017 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 might 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 might be updated, replaced or obsoleted at any time. Its publication as a draft does not imply endorsement by IDPF membership or the IDPF Board. When citing this document, clearly refer to it 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 [EPUB 3.1].

  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 revision of the EPUB specifications began in 2010, with the goal of aligning EPUB more closely with HTML, 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. [Publications 3.0] [Content Docs 3.0] [OCF 3.0] [Media Overlays 3.0]

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. [Publications 3.0.1] [Content Docs 3.0.1] [OCF 3.0.1] [Media Overlays 3.0.1]

  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 [Publications 3.0.1] were moved to this new top-level specification, as was the section on Publication Resources. 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.

[Publications 3.0.1] 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 [Content Docs 3.0.1] to this 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.

[Media Overlays 3.1] also saw its embedded property definitions removed to a separate vocabulary, but was otherwise unchanged structurally.

[Content Docs 3.1] 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.

[OCF 3.1] similarly underwent some minor editorial and structure cleanup, but no sections were added or removed.

  3 EPUB 3.1


Refer to the issue tracker for a complete list of clarifications, typos and other issues in the EPUB 3.1 specification addressed in this revision.

  3.1 Accessibility Support

EPUB 3.1 adds a recommendation that all EPUB Publications conform to the new EPUB Accessibility Specification [EPUB Accessibility]. The accessibility specification makes recommendations for the inclusion of discovery metadata along with [WCAG 2.0] support in content.

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

  3.2 New Core Media Types

EPUB 3.1 adds the WOFF 2.0 and SFNT font formats as Core Media Types [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.

  3.4 Remotely-Hosted Resources

EPUB 3.1 allows fonts and resources used by scripts to be hosted outside the EPUB Container.

  3.5 Removed support for EPUBCFI for linking

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

  4 Packages 3.1


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

  4.1 The refines attribute

Use of the refines attribute [Packages 3.1] is now deprecated. The following attributes have been added to replace the functionality it provided to Reading Systems: duration, opf:alt-rep, opf:authority, opf:file-as, opf:role, opf:scheme and opf:term.


The new opf:scheme attribute is similar in name and purpose to the existing scheme attribute allowed on the meta tag, but is limited to identifying identifier schemes. The attribute was previously allowed in EPUB 2, and compatibility was a consideration in retaining the prefixed name, as was keeping all attributes allowed on the [DCMES] elements in the opf: namespace. These benefits were seen to outweigh any initial authoring confusion that might arise.

  4.2 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 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.

  4.3 Removal of the OPF2 meta Element

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

  4.4 NCX is Marked for Removal

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

  4.5 Removal of the guide Element

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

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

  5 Content Documents 3.1


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

  5.1 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 3.1 remains up to date with the latest recommended versions of these specifications, the dated references have been replaced with undated references in EPUB 3.1. 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.

  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.

  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.

  5.4 Scripting Support Clarifications

EPUB 3.1 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.

  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 altimg attribute.

  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 [HTML] audio and video elements.

  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


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

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

  7 Media Overlays


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

  7.1 Package Metadata Expressions

The deprecation of the refines attribute in the Packages 3.1 specification has impacted the way that Media Overlays metadata gets expressed. In particular, the new duration attribute [Packages 3.1] is now attached to manifest items to indicate their total playback time (the total duration is still set in the package metadata, as before). Narrators can only be identified for the publication as a whole, not for each individual XHTML Content Document.

  8 EPUB Accessibility

The EPUB 3.1 revision introduces the [EPUB Accessibility] specification, which details how to make EPUB Publications accessible and discoverable. This specification leverages the work of [WCAG 2.0] and also adds requirements for EPUB Publications. It is accompanied by the informative [EPUB Accessibility Techniques] 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.

  9 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 in this revision.

  10 Alternate Style Tags

Refer to the issue tracker for a complete list of clarifications, typos and other issues in the Alternate Style Tags specification addressed in this revision.

  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 [EPUB3 Overview].


Normative References

[Content Docs 3.0] EPUB Content Documents 3.0 .

[Content Docs 3.0.1] EPUB Content Documents 3.0.1 .

[Content Docs 3.1] EPUB Content Documents 3.1 .

[Core Media Types] EPUB 3 Core Media Types.

[EPUB 3.1] EPUB 3.1 .

[EPUB Accessibility] EPUB Accessibility .


[Media Overlays 3.0] EPUB Media Overlays 3.0 .

[Media Overlays 3.0.1] EPUB Media Overlays 3.0.1 .

[Media Overlays 3.1] EPUB Media Overlays 3.1 .

[Packages 3.1] EPUB Packages 3.1 .

[Publications 3.0] EPUB Publications 3.0 .

[Publications 3.0.1] EPUB Publications 3.0.1 .

[WCAG 2.0] Web Content Accessibility Guidelines (WCAG) 2.0 . Ben Caldwell, et al.

Informative References

[EPUB Accessibility Techniques] EPUB Accessibility Techniques .

[EPUB3 Overview] EPUB 3.1 Overview .