EPUB 3 Working Group Charter


EPUB 2.1 Working Group Charter – Approved 5/24/10


The mission of the EPUB 2.1 Working Group is to update EPUB 2.0.1 to expand its applicability as a delivery format, and as a cross-Reading System interchange and production format. EPUB has been rapidly adopted as the standard interoperable distribution format for trade eBooks in North American and Europe, and it is desired by the IDPF membership that EPUB should also be adopted, on a global basis, for textbooks, academic, STM, digital magazines, and news delivery, and facilitate increased interoperability across Reading Systems.

Current Industry Problems

There are fourteen main problems that the Working Group is tasked to address in EPUB 2.1:

  1. Need for rich media and interactivity support. EPUB 2.0.1 has an extension mechanism, with provision for fallbacks, but does not intrinsically standardize support for rich media (such as video) and interactivity (programmatic content, such as would be needed to implement a quiz or crossword puzzle). These capabilities are necessary for interactive digital textbooks and digital magazines, and more generally to enable eBooks to evolve into a new medium, rather than simply be digital equivalents of paper books.
  2. Need for enhanced global language support. There is substantial interest in using EPUB in China, Japan, Korea , and other geographies, however it is recognized that at a minimum, requirements for support for the character sets, Ruby markup, and typographic rules needed for reading systems in these geographies (including but not limited to special line-breaking rules and vertical writing direction) are not adequately specified in EPUB 2.0.1.
    Published Minimal Requirements on EPUB for Japanese Text Layout (English)
  3. Need for enhanced article support. The fundamental atomic unit of magazines and newspapers is the article, an entity which is not specifically defined in EBUB 2.0.1.The magazine industry has adopted the PRISM standard for interchange and archival of digital content and it is desirable to support a work flow where PRISM content can be delivered as EPUB.
  4. Need for enhanced metadata support. EPUB 2.0.1 provides basic support for expressing embedded publication metadata. However, native support for standards such as ONIX, RDFa, and others is not yet provided, which has a negative impact on the fidelity of metadata provision. Likewise, PRISM has article-level and inline metadata support that could integrate into EPUB.
  5. Need for a means to convey page-level layouts and target multiple display surface sizes in a single publication. EPUB 2.0.1 lacks any way to specify page-level layouts or dynamically select different layouts based on considerations such as available display area and user-preferred font size. This is a barrier to supporting books with more complex information designs, as well as digital magazines, and even for trade books makes it harder to convey a “house style” (addressing this requirement was requested by the AAP in conjunction with its endorsement of EPUB in May 2008).
  6. Need for enhanced navigation support. There is currently no ability to represent preferred instantiations of navigational elements; as well, presently any rendering of page-to-page navigation as well as Table of Contents and other navigation elements is optional and entirely Reading System-dependent. Version 2.0.1 makes “end user” presentation of the NCX TOC a “should” with statement that the next version will likely transform to a “must” and that other NCX sections may receive similar “upgraded” treatment.
  7. Incomplete alignment with broadly-adopted Web standards. EPUB 2.0.1 is built on numerous horizontal industry standards. However, these building-block standards, and the Web browsers that implement them, are rapidly evolving and the versions of these standards utilized in 2006 when EPUB 2.0 was formulated are no longer current. Since most distributed Reading Systems utilize Web browsers to present content to end users, and many standalone Reading Systems utilize Web browser rendering technologies in their implementations, it is desirable to improve alignment with Web standards as implemented by modern browsers.
  8. Lack of annotation support. There is presently no standard mechanism by which user-generated (aka “post publication”) information such as reading-position, bookmarks, and annotations may be stored and exchanged, which reduces interoperability across Reading Systems. It unclear if annotations should be a separate specification which could “overlay” the other EPUB specs. Note that annotations may wish to be stored and/or transported separately from publication content, and there exist at least two annotation specifications that can work with EPUB as well as other formats (DAISY and Adobe’s).
  9. No native support for mathematics. The lack of a native schema to represent mathematical equations (MathML) limits applicability and interoperability of eBook in the textbook and academic publishing segments.
  10. No native support for book-specific semantics. For academic publishing in particular, the absence of native support for book-specific structures such as glossaries, note reference systems and advanced cross-reference systems pose a limitation that negatively impacts the behavioral repertoire of reading systems.
  11. Insufficient accessibility support. EPUB is well-aligned with the DAISY standard but does not presently incorporate all DAISY features; in particular, there is not explicit support for full synchronization of multiple media types, such as audio and text. The proposed EPUB 2.1 revision will coincide in time with the revision of DAISY (ANSI/NISO Z39.86); the option to further the harmonization of the two standards should be considered.
  12. Insufficient mechanism for adding industry specific extensions. Vertical markets have defined schemas that communicate specific semantics important to their market segment, which presently cannot be handled in an interoperable manner within EPUB.
  13. No clear relationship to approved national and international standards. While EPUB has enjoyed broad adoption, the relationship to national and international standards has not been clearly articulated. In addition, no roadmap has been provided to address these questions in the industry.
  14. No mechanism for including advertising. Currently there is no mechanism to identify and include advertising in publications, which is required in several markets.

Additional minor specification problems and feature requests have been identified in prior EPUB Working Group discussions but deemed out of scope for the EPUB 2.0.1 revision. Some of these will likely be addressed in EPUB 2.1, if feasible within the Working Group time frame. A list of identified issues for future consideration can be found at: EPUB Issues Tracking Database.


Work on EPUB test cases, certification levels, and overall compatibility and compliance with the existing EPUB 2.0.1 specifications is excluded from this Working Group charter, although it is acknowledged to be a very high priority and that members of this Working Group are likely to be involved in parallel efforts (i.e., EPUB Maintenance Working Group) in this area, and that the results of these efforts may affect the deliverables of the Working Group (e.g. the Working Group may decide that test cases, while non-normatively part of the standards specifications, should be required for all new features).

DRM has been agreed to be out of scope for this EPUB 2.1 Working Group.

The IDPF has been interested in ISO certification and it is generally thought that we should move in this direction. The move to ISO will be explored, but is not in scope for this revision. However, the working group will provide recommendations regarding national and international standards.

As always, the Working Group is expected to utilize broadly-adopted building-block open standards wherever feasible, in preference to creation of new technologies, or dependency on proprietary technologies. While the raison d’etre of IDPF work on standards is that horizontal industry standards groups are not prepared to prioritize addressing specific requirements of professional publishing, these broader standards, and in particular Web standards, have orders of magnitude more adoption and therefore “reinventing the wheel” of such standards is explicitly discouraged.

The name “EPUB 2.1” is a placeholder. This enhancement release to EPUB is expected to be a substantive improvement in the capabilities of EPUB, addressing the mission with respect to the enumerated industry problems. As such, it is quite possible that the IDPF Board and Membership will wish to consider this release “EPUB 3.0”. However, the intention is for this release to be completed in a timely manner as per the duration of the Working Group Charter, which timely completion is also critical to achievement of the mission. As such the Working Group is encouraged to consider the scope as limited in the sense that not all conceivable enhancements - perhaps not even solutions to the enumerated problems – can be accomplished in this release. As well, an important goal is to maximize backwards compatibility, i.e. content created for this new release of EPUB should, insofar as possible, be operable on Reading Systems that support EPUB 2.0. The working name “EPUB 2.1” was chosen in keeping with these time-to-market and backwards-compatibility requirements, though “EPUB 3.0” remains possible.

Preliminary Solutions

Adopt HTML5 Features

A potential solution that the Working Group is expected to carefully consider, is for EPUB 2.1 to adopt new features being standardized as part of HTML5. Such features could address, fully or partially, a number of the identified industry problems. This direction would be consistent with the Working Group scope (not reinventing the wheel); however, it is acknowledged that a number of significant issues would need to be resolved.

Page-level layouts and targeting multiple display region sizes

While a solution to problem #5 presents issues in balancing the competing priorities of publishers, Reading System vendors, and end users, the expectation is that the standard must provide for flexibility in this area. The more basic question is what mechanism to use to implement it. There are a number of potential solutions that must be considered to resolve this issue, paying particular attention to existing implementations, interoperability with existing standards and burden on both reading systems and content providers.

Enhance Extension Mechanisms

There are many semantically rich XML schemas and more are expected to emerge that are desirable to support. The WG may wish to consider strengthening the existing extension mechanisms and fallback approach to enable more robust support for add-on schemas.

Duration of Working Group Charter

The Working Group is chartered through May 2011. The Working Group will target an initial working draft (not feature complete) published in September, 2010 that can be a basis for experimental implementations, and aim for a public draft in December 2010 followed in January 2011 with a draft standard for trial use. Final standard recommendation submitted to the Board by May 15, 2011.

Nature of Deliverables

Working group deliverables will include at a minimum:

  • Minutes from Working Group conference calls and face-to-face meetings
  • Working documents such as detailed Requirements documents
  • Draft specifications
  • Validation tool enhancements
  • Sample and test files

Communication and Participation

Working Group deliverables will be made available to all IDPF Members via the IDPF website. Working Group Chairs will be available to Board for updates on the progress of the Working Group. All IDPF members will be encouraged to participate in the Working Group, subject to ability to meet the time commitments required, and additional Invited Experts may be selected by the Working Group Chairs. As EPUB standardization is of interest to the community-at-large, beyond IDPF Members, the Working Group is encouraged to publicly communicate working documents and draft specifications wherever appropriate.

Intellectual Property and IDPF Corporate Documents

All work in the Working Group will be in compliance with the IDPF membership agreement, intellectual property policy, anti-trust documents, policies and procedures and bylaws of the IDPF. The goal is to maintain the open and patent unencumbered status of EPUB.

Work Schedule

  1. Gather and agree on detailed requirements to achieve scope of charter
  2. Consider proposals for meeting requirements and determine direction
  3. Write and review initial (not complete) working draft specification
  4. Iterate and refine based on comments and experience from experimental implementers.
  5. Publish feature complete public draft.
  6. Publish draft standard for trial use.
  7. Publication of final specification for approval via IDPF output process

Meeting Schedule

Weekly or more frequent 1-hour teleconferences, with at least two (probably 3) face-to-face meetings.


The EPUB 2.1 Working Group will spend a maximum of $20,000 USD; primarily to support the anticipated face-to-face meetings and potentially sub-group meetings.

Estimated Time Commitment for Working Group Members

EPUB 2.1 Working Group members should be prepared to attend weekly or more frequent 1-hour teleconference calls, and actively participate in email discussions. In addition, Working Group members are expected to attend two or more face–to-face meetings. Face to face meetings are 2 or three day conferences and usually take place in New York City. Travel expenses are not paid for, but food and meeting space is provided during the meetings.

Working Group members are also expected to volunteer additional time for technical research, specification drafting and other activities pursued by the Working Group. This off-call, and off-face-to-face time investment should range from 3-10+ hours per week during the height of specification design and drafting.

Working Group Leadership

Chair: Markus Gylling

Vice Chair: Garth Conboy

Co-Vice Chair: Brady Duga

Secretary: Bill McCoy

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