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 specification, EPUB 3.1, defines a distribution and interchange format for digital publications and
documents. The EPUB® format provides a means of representing, packaging and encoding structured and
semantically enhanced Web content — including HTML, CSS, SVG and other resources — for distribution in a
single-file container.
EPUB has been widely adopted as the format for digital books (ebooks), and EPUB 3.1 continues to increase
the format's capabilities in order to better support a wider range of publication requirements, including
complex layouts, rich media and interactivity, and global typography features. The expectation is that the
EPUB 3.1 format will be utilized for a broad range of content, including books, magazines and educational,
professional and scientific publications.
EPUB 3.1 is modular in nature: it consists of a family of specifications that define the core features and
functionality of the standard. This specification represents the primary entry point to standard, but the
specifications listed in Specifications are all a part of EPUB 3.1. An index to key concepts and definitions defined across these specifications is
provided at the end of this specification.
The informative [EPUB3 Overview] provides a general introduction to EPUB 3.1. A list of
technical changes from EPUB 3.0.1, the previous version of the standard, is also available in the informative
[EPUB3 Changes].
1.2 Terminology
The following terms are specific to EPUB 3.1. They are capitalized wherever used.
Only the first instance of a term in a section is linked to its definition.
Author
The person(s) or organization responsible for the creation of an EPUB Publication.
The Author is not necessarily the creator of the content.
A collection of one or more Renditions that conform to this
specification, packaged in an EPUB Container.
An EPUB Publication typically represents a single intellectual or artistic work, but this specification
does not circumscribe the nature of the content.
EPUB Reading System (or Reading System)
A system that processes EPUB Publications for presentation to
a user in a manner conformant with this specification.
An XML document that associates the XHTML Content Document with pre-recorded
audio narration in order to provide a synchronized playback experience, as defined in [Media Overlays 3.1].
A resource that contains content or instructions that contribute to the logic and rendering of at least one
Rendition of an EPUB Publication. In the absence of this
resource, the EPUB Publication might not render as intended by the Author. Examples
of Publication Resources include a Rendition's Package Document, EPUB Content Document, CSS Style Sheets, audio, video, images, embedded fonts and
scripts.
With the exception of the Package Document itself, the Publication Resources necessary to render a
Rendition are listed in that Rendition's manifest[Packages 3.1] and bundled in the EPUB Container file (unless specified otherwise
in Publication Resource Locations).
Examples of resources that are not Publication Resources include those identified by the Package Document
link[Packages 3.1] element and those identified in
outbound hyperlinks that resolve to Remote Resources (e.g.,
referenced from the href attribute of an [HTML]a
element).
Release Identifier
The Release Identifier allows any instance of an EPUB Publication to be compared
against another to determine if they are identical, different versions, or unrelated.
The Unique Identifier is the primary identifier for an EPUB Publication, as
identified by the unique-identifier[Packages 3.1] attribute. The Unique Identifier can be shared by
one or more Renditions of the same EPUB Publication.
Significant revision, abridgement, etc. of the content requires a new Unique Identifier.
The following typographic conventions are used in this specification:
markup
All markup (elements, attributes, properties), code (JavaScript, pseudo-code), machine-readable values
(string, characters, media types) and file names are in red monospace font.
markup link
Links to markup and code definitions are in underlined red monospace font.
http://www.idpf.org/
URIs are in navy blue monospace font.
hyperlink
Hyperlinks are underlined and blue.
[reference]
Normative and informative references are enclosed in square brackets.
Term
Terms defined in the Terminology are in capital case.
Term Link
Links to term definitions have a dotted blue underline.
Normative element, attribute and property definitions are in blue boxes.
Informative markup examples are in light gray boxes.
note
Informative notes are in green boxes with a "Note" header.
caution
Informative cautionary notes are in red boxes with a "Caution" header.
1.4 Conformance Statements
The keywords MUST, MUST NOT,
REQUIRED, SHALL, SHALL NOT,
SHOULD, SHOULD NOT, RECOMMENDED,
MAY, and OPTIONAL in this document are to be interpreted as
described in [RFC2119].
All sections and appendixes of this specification are normative except where identified by
the informative status label "This section is informative". The application of informative
status to sections and appendixes applies to all child content and subsections
they contain.
All examples in this specification are informative.
2 Organization
2.1 Specifications
The EPUB 3.1 standard is modular in nature, with core features and functionality defined across a family of
sub-specifications.
This specification represents the top-most specification in the family. It includes the conformance
requirements for both EPUB Publications (the product of the
standard) and EPUB Reading Systems (the applications that
consume EPUB Publications and present their content to users).
The other specifications that comprise EPUB 3.1 are as follows:
These specifications represent the formal list recognized as belonging to EPUB 3.1, and that contain
functionality referenced as part of the standard.
The IDPF has also developed a set of specifications that complement the core functionality of EPUB 3.1, but
but whose support in Reading Systems and use in authoring is optional:
EPUB Previews[Previews] — describes how preview content can be included in EPUB
Publications.
EPUB Region-Based
Navigation[Region Nav] — introduces conventions for region-based navigation through a
visual rendition of an EPUB Publication based on regions of interest.
New functionality is also added periodically through the development of extension specifications. Features
and functionality defined outside of core revisions to the standard, while not formally recognized in this
specification, are nonetheless available for use by Authors and Reading
System developers (but are not stable until they reach the status of Recommended
Specifications).
2.2 Road Map
This section is informative
This section reviews the organization of the EPUB specifications through the central product they define:
the EPUB Publication.
An EPUB Publication consists of one or more Renditions of its
content, each of which is represented by what is called an EPUB Package. An EPUB
Package consists of all the resources needed to render the content. The key file among these is the Package Document, which includes all the metadata used by Reading Systems to present the EPUB Publication to the user
(e.g., the title and author for display in a bookshelf, as well rendering metadata such as whether content
has a fixed layout or can be reflowed). It also provides a complete manifest of resources, and includes a
spine that lists the sequence to render
documents in as a user progresses through the content.
An EPUB Package also include another key file called the EPUB Navigation Document. This document provides critical
navigation capabilities, such as the table of contents, that allow users to quickly and easily navigate the
content.
The requirements for EPUB Packages are defined in [Packages 3.1].
The EPUB Publication's resources are bundled for distribution in a ZIP-based archive with the file
extension .epub. As conformant ZIP archives, EPUB Publications can be unzipped by many
software programs, simplifying both their production and consumption.
The container format not only provides a means of determining that the zipped content represents an EPUB
Publication (the mimetype file), but also provides a universally-named directory of
informative resources (/META-INF). Key among these resources is the
container.xml file, which directs Reading Systems to the available Package
Documents.
The following example visually represents the structure of the EPUB format.
The structure and containment of an EPUB Publication is only one half of the format, the other half being
the content that gets presented to users. This content is built on the Open Web Platform and comes in two
flavours: XHTML and SVG. Called EPUB Content Documents, these documents typically reference many additional resources required
for their proper rendering, such as images, audio and video clips, scripts and style sheets.
Detailed information about the rules and requirements for the production of EPUB Content Documents is
provided in [Content Docs 3.1], and accessibility requirements are defined in [EPUB Accessibility].
Media Overlay
Documents complement EPUB Content Documents. They provide declarative markup for synchronizing
the text in EPUB Content Documents with prerecorded audio. The result is the ability to create a read-aloud
experience where text is highlighted as it is narrated. Media Overlay Documents are defined in [Media Overlays 3.1].
While conceptually simple, an EPUB Publication is more than just a collection of HTML pages and dependent
assets in a ZIP package as presented here. Additional information about the primary features and
functionality that EPUB Publications provide to enhance the reading experience is available from the
referenced specifications, and a more general introduction to the features of EPUB 3.1 is provided in the
informative [EPUB3 Overview].
It may support an arbitrary set
of Foreign Resource
types, and must process fallbacks for unsupported Foreign
Resources as defined in Foreign Resources if not.
It is recommended that Reading Systems support at least one of the [H.264] and [VP8] video codecs, but this is not a conformance requirement
– a Reading System might support other video codecs, or none at all. Authors and
Reading System developers need to take into consideration factors such as breadth of
adoption, video playback quality, and technology usage royalty requirements when making a
choice to include or implement video in either format, or both.
Accessibility
It should meet the accessibility
requirements for Reading Systems in [EPUB Accessibility].
Backward Compatibility
It must attempt to process
an EPUB Publication whose version is lower than "3.1".
EPUB Publications with older version numbers will not always
render exactly as intended unless processed according to their respective specifications. Reading
Systems should support such EPUB Publications as defined by
those specifications.
Forward Compatibility
It should attempt to
process any given Rendition of an EPUB Publication whose Package Document
version attribute designates a version higher than "3.1".
Authors are free to use both
types of resources to construct their EPUB Publications, but need to be aware that some Reading Systems
might not render the Foreign Resources they use.
As EPUB Publications are designed to be fully consumable on any compliant Reading System, a system of
fallbacks is therefore necessary to ensure that the use of Foreign Resources does not impact on the
ability of the user to consume the content. This section lays out the set of Core Media Types that are supported across Reading Systems and identifies fallback mechanisms that can be used to satisfy the
consumability requirement.
When a Foreign Resource is included in the spine or directly rendered in its native
format in an EPUB Content Document, a Core Media Type fallback must be
included. Fallbacks take one of the two following forms:
intrinsic fallback mechanisms provided by the format (e.g., ability to provide more than one
media type or to display an alternate embedded message when a media type cannot be rendered).
Refer to the [HTML] and [SVG] specifications for the
intrinsic fallback capabilities their elements provide.
manifest fallbacks[Packages 3.1] are a feature of the Package Document that create a fallback chain to a Core
Media Type Resources. They are used to create fallbacks for Foreign Resources in the spine[Packages 3.1] and when intrinsic
fallback capabilities are not available (e.g., for the [HTML]img element).
Video resources may be
located outside the EPUB Container.
Resources retrieved by scripts may be located outside the EPUB Container, but the [HTML] and [SVG]script elements must not reference Remote Resources to ensure availability at runtime (i.e.,
from their src or href attributes, respectively).
Font resourcesmay be located outside the EPUB Container.
The following example shows a reference to an audio file in an XHTML Content Document that is located inside the EPUB Container.
<audio src="audio/ch01.mp4" controls="controls"/>
The following example shows a reference to an audio file in an XHTML Content Document that is located
outside the EPUB Container.
Authors are encouraged to locate audio, video and script resources inside the EPUB Container whenever
feasible to allow users access to the entire presentation regardless of connectivity status.
Features defined in this specification and its siblings are occasionally removed if they are no longer needed
or have been replaced by another feature. Prior to removal, the features are marked as deprecated or superseded as an early warning to the EPUB community.
A deprecated feature is one that is in the process of being removed from the current version of the
specification, while a superseded feature is one that is being retained only for authoring content compatible
with an older version.
If a feature is marked as deprecated, the following hold
true:
The feature will be removed in a future version of the specification. The feature is marked as
deprecated in order to give Authors and EPUB Reading System
developers time to prepare for removal.
It is strongly recommended that Authors discontinue use of the
feature in their EPUB
Publications.
Reading Systems must continue to support the feature as it is defined
until it is formally removed.
Validation tools must alert Authors that inclusion of the feature is
deprecated when encountered in an EPUB Publication. It is recommended
that the alert be lower in severity than an error or warning.
If a feature is marked as superseded, the following hold
true:
The superseded feature may be removed in a future version of the
specification, but there is no definite timeline for removal.
Authors may include the superseded feature for compatibility with
older versions of the specification.
Reading Systems must not support the superseded feature in content
that conforms to the current version of the specification.
Validation tools must not alert Authors about the presence of the
superseded feature in an EPUB Publication, as it is valid for backwards compatibility. Validation tools
must alert Authors if the superseded feature is not conformant to
its definition or otherwise breaks a usage requirement.
A feature that is superseded and marked for removal differs from a superseded feature in the following ways:
The feature will be removed in a future version of the specification.
Validation tools must alert Authors about the presence of superseded
features that are marked for removal. It is recommended that the alert
be given the same severity as deprecated features.
Index
This index is informative
This index identifies where key concepts are defined in EPUB 3.1, including element, attribute and property
definitions.
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:
Gylling, Markus(International Digital Publishing Forum)Chair (until August 2016)
Siegman, Tzviya(John Wiley & Sons)Chair
Conboy, Garth(Google Inc.)Vice-chair; Chair (beginning August 2016)
Duga, Brady(Google Inc.)Vice-chair
Active members of the working group included:
IDPF Members
Albert, Paolo(PubCoder)
Audrain, Luc(Hachette Livre)
Bailey, Brent(Elsevier)
Baker, Mike(Houghton Mifflin Harcourt)
Balakrishnan, Ramu(MPS Limited)
Belfanti, Paul(Pearson)
Bell, Graham(EDItEUR)
Bogan, Robert(Baker & Taylor)
Bowers, Micah(Bluefire Productions)
Burrows, Phil(VitalSource/Ingram Content Group)
Challman, Lauren(Kaplan Publishing)
Cho, Yong-Sang(KERIS (Korea Education and Research Information Service))
Cleghorn, Tom(Cambridge University Press)
Comerford, Rachel(Macmillan)
Conboy, Garth(Google)
Corona, Juan(Evident Point)
Cramer, Dave(Hachette Book Group)
Creasy, Keith(American Printing House for the Blind, Inc.)
Davis, Greg(Pearson)
DeMeglio, Marisa(DAISY Consortium)
Deltour, Romain(DAISY Consortium)
Duga, Brady(Google)
Gardeur, Hadrien(Feedbooks)
Geffroy, Jean-Marie(Mantano)
Gusso, Lina(Pearson)
Gylling, Markus(International Digital Publishing Forum (IDPF))
Haase, David(Penguin Random House)
Hanson, Lauren(Kaplan Publishing)
Harris, Eric(VitalSource/Ingram Content Group)
Heinser, Bernhard(Access for All)
Herman, Ivan(W3C)W3C Liaison
Idan, Ori(Helicon Books)
Jay, Michael(Educational Systemics)
Johnson, Rick(VitalSource/Ingram Content Group)
Jung, Eunmi(KERIS (Korea Education and Research Information Service))
Kanai, Takeshi(Sony)
Kasdorf, Bill(Apex CoVantage)
Keating, Patrick(Bluefire Productions)
Kennedy, Naomi(Penguin Random House)
Kerscher, George(DAISY Consortium)
Khramov, Yuri(Readium)
Kleinfeld, Sanders(O'Reilly)
Koike, Toshiaki(Voyager Japan)
Labordrie, Cyril(EDRLab)
LaPierre, Charles(Benetech)
Leo, Arthic(Amnet Systems)
Levantovsky, Vladimir(Monotype)
Levenson, Yonah(Pearson)
Lin, Beatrice(KERIS (Korea Education and Research Information Service))
Lui, Edwina(Kaplan Publishing)
McCoy, Bill(IDPF)
Mietkiewicz, Elie(Gutenberg Technology)
Mitchell, Chris(Hachette Book Group)
Moua, Nou(Kaplan Publishing)
Murata, Makoto(JEPA EPUB Study Group)
Mussinelli, Christina(Associazione Italiana Editori)
