EPUB 3

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ePub version 3 is the newest version of the standard and has now been recommended by the idpf standards committee. This page will describe some of the features as related to the existing ePub 2.01 version.

Contents

Document Organization

In version 2.01 there were three defining documents, the OPF (Open Packaging Format), the OCF (Open Container Format), and the OPS (Open Publications Structure). The OPS referenced a DAISY standard for the NCX file. The new 3.0 standard has 4 defining documents with new names. The OPF becomes the ePub Publications standard. The OCF remains the same and the OPS received the most changes to become the ePub Content Documents. This now includes the old NCX specifications which are no longer used. A fourth document is concerned with Media Overlays and is a new feature of ePub version 3.

Open Container Format

An ePub file continues to be a self contained document with everything contained in one zip file. In 2.0 the access outside with links was not defined but this omission has been addressed in 3.0 to limit the access to specific cases outside the zip file.

Publications standard

The version 2.01 standard remains basically in tact with a few additions. The dcterms:modified has been added to provide a solution for consistent publication identifiers. The metadata elements have been expanded to permit descriptions to be targeted at specific portions of a document as well as the whole document. There is a new link entry that can be used to reference external meta data sources. A new properties entry allows defining publication resources.

The Content Documents

This is the biggest area of change.

  • HTML5 has been adopted as the XHTML format. DTBook is no longer supported as an option for ePub.
  • SVG documents can now appear in the spine. They no longer have to be inside an XHTML document.
  • MathML is now a supported format.
  • Semantic Inflection
  • Content switching was introduced in OPS 2 but is now simplified.

Navigation

An internal navigation syntax is defined for ePub 3. It has a human- and machine-readable grammar for publication-wide navigation information and is based on the HTML5 nav element. In this way it is more like an inline TOC in a book since it is an XHTML document. An example follows for a top level "toc" 

<nav epub:type="toc" id="toc">
  <h1>Table of contents</h1>
  <ol>
    <li>
      <a href="chap1.xhtml">Chapter 1</a>
      <ol>
        <li>
          <a href="chap1.xhtml#sec-1.1">Chapter 1.1</a>
          <ol hidden="">
            <li>
              <a href="chap1.xhtml#sec-1.1.1">Section 1.1.1</a>
            </li>
            <li>
              <a href="chap1.xhtml#sec-1.1.2">Section 1.1.2</a>
            </li>
          </ol>
         </li>
         <li>
           <a href="chap1.xhtml#sec-1.2">Chapter 1.2</a>
         </li>
       </ol>
     </li>
    <li>
      <a href="chap2.xhtml">Chapter 2</a>
    </li>
  </ol>
 </nav>

The top level is indicated by a type of "toc". There can only be one instance in a document. The items are in ordered lists showing the flow of the document. All sections are expected to be present although some can be suppressed from the visual display by using the "hidden" tag as show for the 3rd level. Nav elements can reference other nav elements in secondary lists such as the 'lot' list of tables or 'loi' list of illustrations.

Note that an toc.ncx file will be permitted to provide backward compatibility for existing readers.

Linking

There are planned to be several methods of linking. The first to be defined is listed.

  • ePubCFI is a newly defined linking scheme. It provides for a method of linking to a location inside an ePub from somewhere outside the document. It requires specific knowledge of the content. It makes use of id's defined in the document as well as counting of locations. It needs knowledge of the code view.

Scripting

Scripting is now supported with specific limitations to make it robust even if the reading application doesn't support it.

CSS

EPUB 3 defines a profile of CSS based on CSS 2.1 with added modules from CSS3. All of CSS 2.1 are applicable except:

  • The fixed value of the position property is not part of the EPUB 3 CSS Profile.
  • The direction and unicode-bidi properties must not be included in an EPUB Style Sheet.
  • language should not be set is CSS, it should be done in HTML5 statements.
  • The CSS must be UTF-8 or UTF-16 encoded

CSS3 specific items include:

  • The EPUB 3 CSS Profile includes @font-face rules and descriptors as defined in the CSS3 Fonts Module Level 3 with the following descriptors:
    • font-family
    • font-style
    • font-weight
    • src
    • unicode-range
  • CSS 3.0 Speech module is used with the following additions:
    • -epub-cue
    • -epub-pause
    • -epub-rest
    • -epub-speak
    • -epub-speakability
    • -epub-voice-family

Embedded Fonts

With and without Obfuscation. Support for OpenType and WOFF type fonts are required.

Media Overlays

HTML5 adds video and audio elements directly but there is additional support in ePub 3 with a defined format and processing model for publication-wide synchronization of text and audio. Multiple features to assist Text-to-Speech (TTS) engines have been added.

Systems that support audio playback must support MP3 audio and should support MP4 AAC LC audio. SMIL is required to control the audio insertion and synchronize the data.

Any EPUB Content Document associated with a Media Overlay may contain embedded media such as video, audio, and images. The Media Overlay text element may be used in such instances to reference the embedded media by its ID.

To make the Media overlay work the file pointers must be in the manifest. The reading system must show the appropriate page on the screen while the audio is playing. The user can navigate the document normally and the appropriate media will automatically keep pace. There could also be audio or video elements in the ePub file that are not contained within the media overlay. They are not synchronized. The user interface should provide media controls for these items.

For more information

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