EPUB® 3 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.

This specification defines the authoring requirements for EPUB Publications and represents the third major revision of the standard.

Introduction

Overview

EPUB 3 has been widely adopted as the format for digital books (ebooks), and this revision continues to increase the format's capabilities to better support a wider range of publication requirements, including complex layouts, rich media and interactivity, and global typography features. The expectation is that publishers will utilize the EPUB 3 format for a broad range of content, including books, magazines, and educational, professional, and scientific publications.

This specification represents the core of EPUB 3 and includes the conformance requirements for EPUB Publications — the product of the standard. The other specifications that comprise EPUB 3 are as follows:

These specifications represent the formal list recognized as belonging to EPUB 3 and that contain functionality normatively referenced as part of the standard. The development of extension specifications periodically adds new functionality to EPUB Publications. Features and functionality defined outside of core revisions to the standard, while not formally recognized in this specification, are nonetheless available for EPUB Creators and Reading System developers to use.

The informative EPUB 3 Overview [[EPUB-OVERVIEW-33]] provides a general introduction to EPUB 3. A list of technical changes from the previous version is also available in the change log.

Organization

This section reviews the organization of the EPUB specifications through the central product they define: the EPUB Publication.

An EPUB Publication is typically represented by a single Package Document. This document includes metadata used by Reading Systems to present the content to the user, such as the title and author for display in a bookshelf as well as rendering metadata (e.g., whether the content is reflowable or has a fixed layout). It also provides a manifest of resources and includes a spine that lists the default sequence in which to render documents as a user progresses through the content. Refer to for the requirements for the Package Document.

An EPUB Publication also includes another key file called the EPUB Navigation Document. This document provides critical navigation capabilities, such as the table of contents, that allow users to navigate the content quickly and easily. Refer to for more information about this document.

The actual content of an EPUB Publication — what users are presented with when they begin reading — is built on the Open Web Platform and comes in two flavors: 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.

Refer to for detailed information about the rules and requirements to produce EPUB Content Documents, and [[EPUB-A11Y-11]] for accessibility requirements.

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 Reading Systems highlight the text as it is narrated. Refer to for the definition of Media Overlay Documents.

A ZIP-based archive with the file extension .epub bundles the EPUB Publication's resources for distribution. 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. Refer to for more information about the Container format.

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 is provided in the informative [[EPUB-OVERVIEW-33]].

Refer to [[EPUB-RS-33]] for the processing requirements for Reading Systems. Although it is not necessary that EPUB Creators read that document to create EPUB Publications, an understanding of how Reading Systems present the content can help craft publications for optimal presentation to users.

Relationship to Other Specifications

Relationship to HTML

The [[HTML]] standard is continuously evolving — there are no longer versioned releases of it. That standard, in turn, references various technologies that continue to evolve, such as MathML, SVG, CSS, and JavaScript.

The benefit of this approach for EPUB is that EPUB Publications always keep pace with changes to the Web without the need for new revisions. EPUB Creators, however, must keep track of the various changes to HTML and the technologies it references to ensure they keep their processes up to date.

As HTML evolves, it is possible that previously-valid features may become obsolete or be removed. In general, however, the removal of features typically only occurs when serious issues arise with them (e.g., lack of support in browsers, security issues).

The XHTML profile defined by this specification inherits all definitions of semantics, structure and processing behaviors from HTML unless otherwise specified.

In addition, this specification defines a set of extensions to the [[HTML]] document model that EPUB Creators may include in XHTML Content Documents.

Relationship to SVG

This specification does not reference a specific version of [[SVG]], but instead uses an undated reference. Whenever there is any ambiguity in this reference, the latest recommended specification is the authoritative reference.

This approach ensures that EPUB will always keep pace with changes to the SVG standard. EPUB Creators, however, must keep track of changes to the SVG standard to ensure they keep their processes up to date.

As SVG evolves, features previously-valid features may become obsolete or be removed. The Working Group anticipates the W3C will make any such changes carefully to ensure minimal disruption, but in the case of a backwards-incompatible revision the Working Group could revisit the use of an undated reference.

Relationship to CSS

EPUB 3 supports CSS as defined by the CSS Working Group Snapshot [[CSSSnapshot]]. EPUB 3 also maintains some prefixed CSS properties, to ensure consistent support for global languages.

Relationship to SMIL

This specification relies on a subset of [[SMIL3]], from which the Media Overlays elements and attributes defined in are derived.

Terminology

This specification defines the following terms specific to EPUB 3. They appear capitalized wherever used.

Only the first instance of a term in a section links to its definition.

Codec

Codec refers to content that has intrinsic binary format qualities, such as video and audio media types designed for optimum compression or that provide optimized streaming capabilities.

Content Display Area

The area within the Viewport dedicated to the display of EPUB Content Documents. The Content Display Area excludes any borders, margins, headers, footers, or other decoration a EPUB Reading System might inject into the Viewport.

In the case of synthetic spreads, the Viewport contains two Content Display Areas.

Core Media Type Resource

A Publication Resource that does not require the provision of a fallback (cf. Foreign Resource).

EPUB Container
OCF ZIP Container

The ZIP-based packaging and distribution format for EPUB Publications defined in .

EPUB Container and OCF ZIP Container are synonymous.

EPUB Content Document

A Publication Resource with an XHTML or SVG media type that contains all or part of the content of an EPUB Publication (i.e., the textual, visual and/or audio content). These resources must conform to their respective XHTML or SVG definitions to be used in the spine or be referenced from another EPUB Content Document.

An EPUB Content Document is a Core Media Type Resource, so EPUB Creators can include it without the provision of fallbacks.

EPUB Creator

The person(s) or organization responsible for the creation of an EPUB Publication.

Depending on the process used to produce EPUB Publications, EPUB Creator may sometimes refer to responsibilities of the organization (e.g., the publisher) or the individuals preparing the publication (e.g., technical editors).

Previous versions of this specification referred to the EPUB Creator as the Author.

EPUB Navigation Document

A specialization of the XHTML Content Document that contains human- and machine-readable global navigation information. The EPUB Navigation Document conforms to the constraints expressed in .

EPUB Publication

A logical document entity consisting of a set of interrelated resources packaged in an EPUB Container.

An EPUB Publication typically represents a single intellectual or artistic work, but this specification does not restrict 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.

File Name

The name of any type of file within an OCF Abstract Container, whether a directory or a file within a directory.

Fixed-Layout Document

An EPUB Content Document with fixed dimensions directly referenced from the spine. Fixed-Layout Documents are designated pre-paginated in the Package Document, as defined in .

Foreign Resource

A Publication Resource that is not a Core Media Type Resource. Foreign Resources are subject to the fallback requirements defined in .

Local Resource

A resource that is located inside the EPUB Container.

Refer to for media type specific rules for resource locations.

Manifest

The section of the Package Document that lists the Publication Resources.

Refer to for more information.

Media Overlay Document

An XML document that associates the XHTML Content Document with pre-recorded audio narration to provide a synchronized playback experience, as defined in .

Non-Codec

Non-Codec refers to content types that benefit from compression due to the nature of their internal data structure, such as file formats based on character strings (for example, HTML, CSS, etc.).

OCF Abstract Container

The OCF Abstract Container defines a file system model for the contents of the OCF ZIP Container, as defined in .

Package Document

A Publication Resource that describes the rendering of an EPUB Publication, as defined in . The Package Document carries meta information about the EPUB Publication, provides a manifest of resources and defines a default reading order.

Path Name

For a given directory within the OCF Abstract Container, the string holding all directory File Name in the full path concatenated together with a / (U+002F) character separating the directory File Names.

For a given file within the OCF Abstract Container, the Path Name is the string holding all directory File Names concatenated together with a / character separating the directory File Names, followed by a / character and then the File Name of the file.

Publication Resource

A resource that contains content or instructions that contribute to the logic and rendering of an EPUB Publication. In the absence of this resource, Reading Systems may not render the EPUB Publication as the EPUB Creator intends. Examples of Publication Resources include the Package Document, EPUB Content Document, CSS Style Sheets, audio, video, images, embedded fonts, and scripts.

EPUB Creators typically list Publication Resources in the Package Document manifest and bundle them in the EPUB Container, with the following exceptions:

  • they do not have to list resources encoded as data URLs in the manifest; and

  • they may locate resources listed in outside the EPUB Container.

Examples of resources that are not Publication Resources include those identified in Package Document link elements and those identified in outbound hyperlinks that resolve to Remote Resources (e.g., referenced from the href attribute of an [[HTML]] a element).

Remote Resource

A resource that is located outside of the EPUB Container, typically, but not necessarily, online.

Refer to for media type specific rules for resource locations.

Root Directory

The root directory represents the base of the OCF Abstract Container file system. This directory is virtual in nature: an EPUB Reading System may or may not generate a physical root directory for the contents of the OCF Abstract Container if it unzips the contents.

Scripted Content Document

An EPUB Content Document that includes scripting or an XHTML Content Document that contains [[HTML]] forms.

Refer to for more information.

Spine

An ordered list of Publication Resources in the Package Document, typically EPUB Content Documents, that represent the default reading order.

Refer to for more information.

SVG Content Document

An EPUB Content Document that conforms to the constraints expressed in .

Synthetic Spread

The rendering of two adjacent pages simultaneously on a device screen.

Text-to-Speech (TTS)

The rendering of the textual content of an EPUB Publication as artificial human speech using a synthesized voice.

Top-level Content Document

An EPUB Content Document referenced from the spine, whether directly or via a fallback chain.

Unique Identifier

The primary identifier for an EPUB Publication in the Package Document, as identified by the unique-identifier attribute.

Significant revision, abridgement, etc. of the content requires a new Unique Identifier.

Viewport

The region of an EPUB Reading System in which an EPUB Publication is rendered visually to a user.

XHTML Content Document

An EPUB Content Document that conforms to the profile of [[HTML]] defined in .

XHTML Content Documents use the XHTML syntax defined in [[HTML]].

Authoring Shorthands

Prefixes

In Package Document metadata examples, reserved prefixes are used without declaration.

Namespaces

For convenience, the following namespace prefixes [[XML-NAMES]] are used in this specification without explicitly being declared. EPUB Creators MUST declare these prefixes to use them in an EPUB Content Document.

prefix URI
epub http://www.idpf.org/2007/ops
ssml https://www.w3.org/2001/10/synthesis

EPUB Publications

Conformance Criteria

An EPUB Publication:

In addition, all Publication Resources MUST adhere to the requirements in .

The rest of this specification covers specific conformance details.

Publication Resources

Core Media Types

Introduction

An EPUB Publication typically consists of many Publication Resources. These resources are divided into two categories: those that do not require fallbacks (Core Media Type Resources) and those that do (Foreign Resources).

The Working Group typically only includes formats as Core Media Type Resources when they have broad support in web browser cores — the rendering engines that EPUB 3 Reading Systems build upon. They are an agreement between Reading System developers and EPUB Creators to ensure the predictability of rendering of EPUB Publications.

Inclusion as a Core Media Type Resource does not mean that all Reading Systems will support the rendering of a resource, however. Reading Systems support also depends on the capabilities of the application (e.g., a Reading System with a Viewport must support image Core Media Type Resources, but a Reading System without a Viewport does not). Refer to Core Media Types [[EPUB-RS-33]] for more information about which Reading Systems rendering capabilities require support for which Core Media Type Resources.

Foreign Resources come with no guarantee of rendering support, which is why they require a fallback to a Core Media Type Resource. EPUB Publications should be fully consumable on any conforming Reading System, so providing a fallback is necessary to ensure that the use of Foreign Resources does not impact on the ability of the user to consume the content.

This section lists the set of Core Media Type Resources and identifies fallback mechanisms used to satisfy the consumability requirement.

EPUB also exempts some [[HTML]] elements from support requirements (see ). Resources referenced from these elements are neither Core Media Type Resources nor Foreign Resources — they do not require fallbacks, but they also have no support requirements.

Supported Media Types

EPUB Creators may include Publication Resources that conform to the following MIME media type [[RFC2046]] specifications in EPUB Publications without fallbacks.

The columns in the following table represent the following information:

  • Media Type—The MIME media type [[RFC2046]] used to represent the given Publication Resource in the manifest.

    If the table lists more than one media type, the first one is the preferred media type. EPUB Creators should use the preferred media type for all new EPUB Publications.

  • Content Type Definition—The specification to which the given Core Media Type Resource must conform.
  • Applies to—The Publication Resource type(s) that the Media Type and Content Type Definition applies to.
Media Type Content Type Definition Applies to
Images
image/gif [[GIF]] GIF Images
image/jpeg [[JPEG]] JPEG Images
image/png [[PNG]] PNG Images
image/svg+xml SVG Content Documents SVG documents
image/webp [[WebP-Container]], [[WebP-LB]] WebP Images
Audio
audio/mpeg [[MP3]] MP3 audio
audio/mp4 [[MPEG4-Audio]], [[MP4]] AAC LC audio using MP4 container
audio/opus [[RFC7845]] OPUS audio using OGG container
Video
EPUB 3 allows EPUB Creators to include any video codecs without fallbacks, although none are technically Core Media Type Resources. Although the Working Group recommends that Reading Systems support at least one of the H.264 [[?H264]] and VP8 [[?RFC6386]] video codecs, support is not a conformance requirement — a Reading System might support other video codecs, or none at all. EPUB Creators must consider factors such as breadth of adoption, video playback quality, and technology usage royalty requirements when making a choice to include video in either format, or both.
Tracks
EPUB Creators can include any kind of audio or video track (for example, [[?WebVTT]] captions, subtitles and descriptions) without a fallback. Refer to for more information.
Style
text/css CSS Style Sheets CSS Style Sheets.
Fonts
EPUB 3 allows EPUB Creators to include any font resource without a fallback, as CSS already defines fallback rules for fonts. Refer to the Reading System support requirements for fonts [[EPUB-RS-33]] for more information.
  1. font/ttf
  2. application/font-sfnt
[[TrueType]] TrueType fonts
  1. font/otf
  2. application/font-sfnt
  3. application/vnd.ms-opentype
[[OpenType]] OpenType fonts
  1. font/woff
  2. application/font-woff
[[WOFF]] WOFF fonts
font/woff2 [[WOFF2]] WOFF2 fonts
Other
application/xhtml+xml XHTML Content Documents XHTML Content Documents that use the XHTML syntax [[HTML]].
  1. application/javascript
  2. application/ecmascript
  3. text/javascript
[[RFC4329]] Scripts.
application/x-dtbncx+xml [[OPF-201]] The legacy NCX.
application/smil+xml Media Overlays EPUB Media Overlay documents
application/pls+xml [[PRONUNCIATION-LEXICON]] Text-to-Speech (TTS) Pronunciation lexicons

Although, OPUS/OGG has good support in Android, MacOS, Windows, and Linux, Apple, starting with iOS 11, only supports the OPUS codec in a CAF container. The working group will monitor support for OPUS in iOS and may remove OPUS as a core media type if the level of support is inadequate.

WebP is currently not defined in a stable specification and its media type has not been registered with IANA. Apple also only supports WebP on macOS 11. The working group will continue to monitor these issues.

Foreign Resources

EPUB Creators MAY include Foreign Resources without a fallback provided they do not reference them from spine itemref elements or directly render them in their native format in EPUB Content Documents (e.g., via [[HTML]] embedded content and [[SVG]] image and foreignObject elements).

This exception allows EPUB Creators to include resources in the EPUB Container that are not for use by EPUB Reading Systems. The primary case for this exception is to allow data files to travel with an EPUB Publication, whether for scripts to use in their constituent EPUB Content Documents or for external applications to use (e.g., a scientific journal might include a data set with instructions on how to extract it from the EPUB Container).

When a Foreign Resource is included in the spine or directly rendered in its native format in an EPUB Content Document, a fallback Core Media Type Resource MUST be included. Fallbacks take one of the following forms:

  • intrinsic fallback mechanisms provided by the host format (e.g., [[?HTML]] elements often provide the ability to reference more than one media type or to display an alternate embedded message when a media type cannot be rendered); or

  • manifest fallbacks.

Manifest fallbacks are a feature of the Package Document that create fallback chains to Core Media Type Resources. They are used to create fallbacks for Foreign Resources in the spine and when intrinsic fallback capabilities are not available (e.g., for the [[HTML]] img element).

Refer to the [[HTML]] and [[SVG]] specifications for the intrinsic fallback capabilities their elements provide.

Resource Locations

EPUB Creators MUST locate all Publication Resources in the EPUB Container, with the following exceptions:

EPUB Creators should locate these resources inside the EPUB Container whenever feasible to allow users access to the entire presentation regardless of connectivity status.

The rules in this section for Publication Resource locations apply regardless of whether the given resource is a Core Media Type Resource or a Foreign Resource.

The inclusion of Remote Resources is indicated via the remote-resources property on the manifest item element.

Data URLs

The data: URL scheme [[RFC2397]] is used to encode resources directly into a URL string. The advantage of this scheme is that it allows EPUB Creators to embed a resource within another, avoiding the need for an external file.

EPUB Creators MAY use data URLs in EPUB Publications provided their use does not result in a Top-level Content Document or top-level browsing context [[HTML]]. This restriction applies to data URLs used in the following scenarios:

  • in manifest item elements referenced from the spine;

  • in the href attribute on [[HTML]] or [[SVG]] a elements (except when inside an iframe element [[HTML]]);

  • in the href attribute on [[HTML]] area elements (except when inside an iframe element);

  • in calls to [[ECMASCRIPT]] window.open or document.open.

The list of prohibited uses for data URLs is subject to change as the respective standards that allow their use evolve.

This restriction on their use is to prevent security issues and also to ensure that Reading Systems can determine where to take a user next (i.e., because these resources are not be listed in the spine).

Resources represented as data URLs are not Publication Resources so are exempt from the requirement for EPUB Creators to list them in the manifest.

EPUB Creators MUST encode Data URLs as Core Media Types or use them where they can provide a fallback (i.e., Data URLs are subject to the foreign resource restrictions).

XML Conformance

Any Publication Resource that is an XML-Based Media Type:

  • MUST be a conformant XML 1.0 Document as defined in Conformance of Documents [[XML-NAMES]].

  • MAY only specify a document type declaration that references an external identifier appropriate for its media type — as defined in — or that omits external identifiers [[XML]].

  • MUST NOT contain external entity declarations in the internal DTD subset [[XML]].

  • MUST NOT make use of XInclude [[XInclude]].

  • MUST be encoded in UTF-8 or UTF-16 [[Unicode]], with UTF-8 as the RECOMMENDED encoding.

The above constraints apply regardless of whether the given Publication Resource is a Core Media Type Resource or a Foreign Resource.

Although EPUB Reading Systems are required to support [[EPUB-RS-33]] the XML `base` attribute [[XMLBase]], [[HTML]] and [[SVG]] are removing support. EPUB Creators should avoid using this feature.

Package Document

Introduction

The Package Document is an XML document that consists of a set of elements that each encapsulate information about a particular aspect of an EPUB Publication. These elements serve to centralize metadata, detail the individual resources, and provide the reading order and other information necessary for its rendering.

The following list summarizes the information found in the Package Document:

  • Metadata — mechanisms to include and/or reference metadata.

  • A manifest — identifies via URL [[URL]], and describes via MIME media type [[RFC4839]], the set of Publication Resources.

  • A spine — an ordered sequence of ID references to top-level resources in the manifest from which Reading Systems can reach or utilize all other resources in the set. The spine defines the default reading order.

  • Collections — a method of encapsulating and identifying subcomponents within the Package.

  • Manifest fallback chains — a mechanism that defines an ordered list of top-level resources as content equivalents. A Reading System can then choose between the resources based on which it is capable of rendering.

An EPUB Publication can reference more than one Package Document, allowing for alternative representations of the content. For more information, refer to

Refer to for information about the file properties of Package Documents.

Package Document Definition

All [[XML]] elements defined in this section are in the http://www.idpf.org/2007/opf namespace [[XML-NAMES]] unless otherwise specified.

Shared Attributes

This section provides definitions for shared attributes (i.e., attributes allowed on two or more elements).

dir

Specifies the base direction [[BIDI]] of the carrying element and its descendants.

Allowed values are:

  • ltr — left-to-right base direction;
  • rtl — right-to-left base direction; and
  • auto — base direction is determined using the Unicode Bidi Algorithm [[BIDI]].

Reading Systems will assume the value auto when EPUB Creators omit the attribute or use an invalid value.

The base direction specified in the dir attribute does not affect the ordering of characters within directional runs, only the relative ordering of those runs and the placement of weak directional characters such as punctuation.

<package … dir="ltr">

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:description, dc:publisher, dc:relation, dc:rights, dc:subject, dc:title, meta and package.

href

A valid URL string [[URL]] that references a resource.

<link rel="record"
      href="meta/9780000000001.xml" 
      media-type="application/marc"/>

Allowed on: item and link.

id

The ID [[XML]] of the element, which MUST be unique within the document scope.

<dc:identifier id="pub-id">urn:isbn:97800000000001</dc:identifier>

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:date, dc:description, dc:format, dc:identifier, dc:language, dc:publisher, dc:relation, dc:rights, dc:source, dc:subject, dc:title, dc:type, item, itemref, link, manifest, meta, package and spine.

media-type

A media type [[RFC2046]] that specifies the type and format of the referenced resource.

<link rel="record"
      href="http://example.org/meta/12389347?format=xmp"
      media-type="application/xml"
      properties="xmp"/>

Allowed on: item and link.

properties

A space-separated list of property values.

Refer to each element's definition for the reserved vocabulary for the attribute.

<item id="nav" 
      href="nav.xhtml" 
      properties="nav"
      media-type="application/xhtml+xml"/>

Allowed on: item, itemref and link.

refines

Establishes an association between the current expression and the element or resource identified by its value. EPUB Creators MUST use as the value a relative-URL-with-fragment string [[URL]] that references the resource or element they are describing.

The refines attribute is OPTIONAL depending on the type of metadata expressed. When omitted, the element defines a primary expression.

When creating expressions about a Publication Resource, the refines attribute SHOULD specify a fragment identifier that references the ID of the resource's manifest entry.

Allowed on: link and meta.

xml:lang

Specifies the language used in the contents and attribute values of the carrying element and its descendants, as defined in section 2.12 Language Identification of [[XML]]. The value of each xml:lang attribute MUST be a well-formed language tag [[BCP47]].

<package … xml:lang="ja">
	…
</package>

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:description, dc:publisher, dc:relation, dc:rights, dc:subject, dc:title, meta and package.

The package Element

The package element is the root element of the Package Document.

Element Name

package

Usage

The package element is the root element of the Package Document.

Attributes
Content Model

In this order:

The version attribute specifies the EPUB specification version to which the given EPUB Publication conforms. The attribute MUST have the value "3.0" to indicate conformance with EPUB 3.

Updates to this specification do not represent new versions of EPUB 3 (i.e., each new 3.X specification is a continuation of the EPUB 3 format). The Working Group is committed to minimizing any changes that would invalidate existing content, allowing the version attribute value to remain unchanged.

The unique-identifier attribute takes an IDREF [[XML]] that identifies the dc:identifier element that provides the preferred, or primary, identifier.

The prefix attribute provides a declaration mechanism for prefixes not reserved by this specification. Refer to for more information.

Metadata Section
The metadata Element

The metadata element encapsulates meta information.

Element Name

metadata

Usage

REQUIRED first child of package.

Attributes

None

Content Model

In any order:

The Package Document metadata element has two primary functions:

  1. to provide a minimal set of meta information for Reading Systems to use to internally catalogue an EPUB Publication and make it available to a user (e.g., to present in a bookshelf).

  2. to provide access to all rendering metadata needed to control the layout and display of the content (e.g., fixed-layout properties).

The Package Document does not provide complex metadata encoding capabilities. If EPUB Creators need to provide more detailed information, they can associate metadata records (e.g., that conform to an international standard such as [[ONIX]] or are created for custom purposes) using the link element. This approach allows Reading Systems to process the metadata in its native form, avoiding the potential problems and information loss caused by translating to use the minimal Package Document structure.

In keeping with this philosophy, the Package Document only has the following minimal metadata requirements: it MUST contain the [[DCTERMS]] title, identifier, and language elements together with the [[DCTERMS]] modified property. All other metadata is OPTIONAL.

The meta element provides a generic mechanism for including metadata properties from any vocabulary. Although EPUB Creators MAY use this mechanism for any metadata purposes, they will typically use it to include rendering metadata defined in EPUB specifications.

See [[EPUB-A11Y-11]] for accessibility metadata recommendations.

Metadata Values

The Dublin Core elements [[DCTERMS]] and meta element have mandatory child text content [[DOM]]. This specification refers to this content as the value of the element in their descriptions.

These elements MUST have non-empty values after leading and trailing ASCII whitespace [[Infra]] is stripped (i.e., they must consist of at least one non-whitespace character).

Whitespace within these element values are not significant. Sequences of one or more whitespace characters are collapsed to a single space [[Infra]] during processing .

DCMES Required Elements
The identifier Element

The [[DCTERMS]] identifier element contains an identifier such as a UUID, DOI or ISBN.

Element Name

dc:identifier

Namespace

http://purl.org/dc/elements/1.1/

Usage

REQUIRED child of metadata.

Attributes
  • id [conditionally required]

Content Model

Text

The EPUB Creator MUST provide an identifier that is unique to one and only one EPUB Publication — its Unique Identifier — in an identifier element. This identifier element MUST specify an id attribute whose value is referenced from the package element's unique-identifier attribute.

Although not static, EPUB Creators should make changes to the Unique Identifier for an EPUB Publication as infrequently as possible. Unique Identifiers should have maximal persistence both for referencing and distribution purposes. EPUB Creators should not issue new identifiers when making minor revisions such as updating metadata, fixing errata, or making similar minor changes.

EPUB Creators MAY specify additional identifiers. The identifiers should be fully qualified URIs.

EPUB Creators MAY use the identifier-type property to indicate that an identifier conforms to an established system or an issuing authority granted it.

The title Element

The [[DCTERMS]] title element represents an instance of a name for the EPUB Publication.

Element Name

dc:title

Namespace

http://purl.org/dc/elements/1.1/

Usage

REQUIRED child of metadata.

Attributes
Content Model

Text

The metadata section MUST contain at least one title element containing the title for the EPUB Publication.

The first title element in document order is the main title of the EPUB Publication (i.e., the primary one Reading Systems present to users).

EPUB Creators should use only a single title element to ensure consistent rendering of the title in Reading Systems.

Although it is possible to include more than one title element for multipart titles, Reading System support for additional title elements is inconsistent. Reading Systems may ignore the additional segments or combine them in unexpected ways.

For example, the following example shows a basic multipart title:

<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
    <dc:title>THE LORD OF THE RINGS</dc:title>
    <dc:title>Part One: The Fellowship of the Ring</dc:title>
    …
</metadata>

The same title could instead be expressed using a single dc:title element as follows:

<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
    <dc:title>
        THE LORD OF THE RINGS, Part One: The Fellowship of the Ring
    </dc:title>
    …
</metadata>

Previous versions of this specification recommended using the title-type and display-seq properties to identify and format the segments of multipart titles (see the Great Cookbooks example). It is still possible to add these semantics but they are also not well supported.

The language Element

The [[DCTERMS]] language element specifies the language of the content of the EPUB Publication.

Element Name

dc:language

Namespace

http://purl.org/dc/elements/1.1/

Usage

REQUIRED child of metadata. Repeatable.

Attributes

id [optional]

Content Model

Text

The metadata section MUST contain at least one language element. The value of each language element MUST be a well-formed language tag [[BCP47]].

Although EPUB Creators MAY specify additional language elements for multilingual Publications, Reading Systems will treat the first language element in document order as the primary language of the EPUB Publication.

Publication Resources do not inherit their language from the dc:language element(s). EPUB Creators must set the language of a resource using the intrinsic methods of the format.

DCMES Optional Elements
General Definition

All [[DCTERMS]] elements except for identifier, language, and title are designated as OPTIONAL. These elements conform to the following generalized definition:

Element Name

contributor | coverage | creator | date | description | format | publisher | relation | rights | source | subject | type

Namespace

http://purl.org/dc/elements/1.1/

Usage

OPTIONAL child of metadata. Repeatable.

Attributes
  • dir [optional] – only allowed on contributor, coverage, creator, description, publisher, relation, rights, and subject.

  • id [optional] – allowed on any element.

  • xml:lang [optional] – only allowed on contributor, coverage, creator, description, publisher, relation, rights, and subject.

Content Model

Text

This specification does not modify the [[DCTERMS]] element definitions except as noted in the following sections.

The contributor Element

The [[DCTERMS]] contributor element is used to represent the name of a person, organization, etc. that played a secondary role in the creation of the content.

The requirements for the contributor element are identical to those for the creator element in all other respects.

The creator Element

The [[DCTERMS]] creator element represents the name of a person, organization, etc. responsible for the creation of the content. EPUB Creators can associate a role property with the element to indicate the function the creator played.

The creator element SHOULD contain the name of the creator as EPUB Creators intend Reading Systems to display it to users.

EPUB Creators MAY use the file-as property to associate a normalized form of the creator's name, and the alternate-script property to represent the creator's name in another language or script.

If an EPUB Publication has more than one creator, EPUB Creators SHOULD specify each in a separate creator element.

The document order of creator elements in the metadata section determines the display priority, where the first creator element encountered is the primary creator.

EPUB Creators SHOULD represent secondary contributors using the contributor element.

The date Element

The [[DCTERMS]] date element MUST only be used to define the publication date of the EPUB Publication. The publication date is not the same as the last modified date (the last time the EPUB Creator changed the EPUB Publication).

It is RECOMMENDED that the date string conform to [[ISO8601]], particularly the subset expressed in W3C Date and Time Formats [[DateTime]], as such strings are both human and machine readable.

EPUB Creators SHOULD express additional dates using the specialized date properties available in the [[DCTERMS]] vocabulary, or similar.

EPUB Publications MUST NOT contain more than one date element.

The subject Element

The [[DCTERMS]] subject element identifies the subject of the EPUB Publication. EPUB Creators SHOULD set the value of the element to the human-readable heading or label, but MAY use a code value if the subject taxonomy does not provide a separate descriptive label.

EPUB Creators MAY identify the system or scheme they drew the element's value from using the authority property.

When a scheme is identified, EPUB Creators MUST associate a subject code using the term property.

The term property MUST NOT be associated with a subject element that does not specify a scheme.

The values of the subject element and term property are case sensitive only when the designated scheme requires.

The type Element

The [[DCTERMS]] type element is used to indicate that the EPUB Publication is of a specialized type (e.g., annotations or a dictionary packaged in EPUB format).

EPUB Creators MAY use any text string as a value.

The former IDPF EPUB 3 Working Group maintained an informative registry of specialized EPUB Publication types for use with this element. This Working Group no longer maintains this registry and does not anticipate developing new specialized publication types.

The meta Element

The meta element provides a generic means of including package metadata.

Element Name

meta

Usage

As child of the metadata element. Repeatable.

Attributes
Content Model

Text

Each meta element defines a metadata expression. The property attribute takes a property data type value that defines the statement made in the expression, and the text content of the element represents the assertion. (Refer to for more information.)

This specification defines two types of metadata expressions that EPUB Creators can define using the meta element:

  • A primary expression is one in which the expression defined in the meta element establishes some aspect of the EPUB Publication. A meta element that omits a refines attribute defines a primary expression.
  • A subexpression is one in which the expression defined in the meta element is associated with another expression or resource using the refines attribute to enhance its meaning. A subexpression might refine a media clip, for example, by expressing its duration, or refine a creator or contributor expression by defining the role of the person.

EPUB Creators MAY use subexpressions to refine the meaning of other subexpressions, thereby creating chains of information.

All the DCMES [[DCTERMS]] elements represent primary expressions, and permit refinement by meta element subexpressions.

The Meta Properties Vocabulary is the default vocabulary for use with the property attribute.

EPUB Creators MAY add terms from other vocabularies as defined in .

The scheme attribute identifies the system or scheme the EPUB Creator obtained the element's value from. The value of the attribute MUST be a property data type value that resolves to the resource that defines the scheme.

Last Modified Date

The metadata section MUST contain exactly one [[DCTERMS]] modified property containing the last modification date. The value of this property MUST be an [[XMLSCHEMA-2]] dateTime conformant date of the form: CCYY-MM-DDThh:mm:ssZ

EPUB Creators MUST express the last modification date in Coordinated Universal Time (UTC) and MUST terminate it with the "Z" (Zulu) time zone indicator.

EPUB Creators should update the last modified date whenever they make changes to the EPUB Publication.

EPUB Creators MAY specify additional modified properties in the Package Document metadata, but they MUST have a different subject (i.e., they require a refines attribute that references an element or resource).

The requirements for the last modification date are to ensure compatibility with earlier versions of EPUB 3 that defined a release identifier [[EPUBPackages-32]] for EPUB Publications.

Manifest Section
The manifest Element

The manifest element provides an exhaustive list of Publication Resources used in the rendering of the content.

Element name

manifest

Usage

REQUIRED second child of package, following metadata.

Attributes

id [optional]

Content Model

item [1 or more]

EPUB Creators MUST list all Publication Resources in the manifest, regardless of whether they are Local or Remote Resources, using item elements.

Note that the manifest is not self-referencing: EPUB Creators MUST NOT specify an item element that refers to the Package Document itself.

Failure to provide a complete manifest of resources may lead to rendering issues. Reading Systems might not unzip such resources or could prevent access to them for security reasons.

This specification supports internationalized resource naming, so elements and attributes that reference Publication Resources accept URLs [[URL]] as their value. For compatibility with older Reading Systems that only accept URIs, EPUB Creators should restrict resource names to the ASCII character set.

The item Element

The item element represents a Publication Resource.

Element Name

item

Usage

As a child of manifest. Repeatable.

Attributes
Content Model

Empty

Each item element identifies a Publication Resource by the URL [[URL]] in its href attribute. EPUB Creators MAY use absolute- or relative-URL string [[URL]], but they MUST ensure each URL is unique within the manifest scope after resolution to an absolute URL [[EPUB-RS-33]].

The Publication Resource identified by an item element MUST conform to the applicable specification(s) as inferred from the MIME media type provided in the media-type attribute. For Core Media Type Resources, EPUB Creators MUST use the media type designated in .

The fallback attribute takes an IDREF [[XML]] that identifies a fallback for the Publication Resource referenced from the item element. EPUB Creators MAY provide fallbacks for Core Media Type Resources (e.g., to provide a static alternative to a Scripted Content Document). Refer to for fallback requirements for Foreign Resources.

The Manifest Properties Vocabulary is the default vocabulary for the properties attribute.

EPUB Creators MAY add terms from other vocabularies as defined in .

EPUB Creators MUST declare all applicable descriptive metadata properties for each Publication Resource in this attribute.

EPUB Creators MUST declare exactly one item as the EPUB Navigation Document using the nav property.

The media-overlay attribute takes an IDREF [[XML]] that identifies the Media Overlay Document for the resource described by this item. Refer to for more information.

The order of item elements in the manifest is not significant. The spine element provides the presentation sequence of content documents.

Examples

The following example shows a manifest that contains only Core Media Type Resources.

<manifest>
    <item id="nav" 
          href="nav.xhtml" 
          properties="nav"
          media-type="application/xhtml+xml"/>
    <item id="intro" 
          href="intro.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c1" 
          href="chap1.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c1-answerkey" 
          href="chap1-answerkey.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c2" 
          href="chap2.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c2-answerkey" 
          href="chap2-answerkey.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c3" 
          href="chap3.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="c3-answerkey" 
          href="chap3-answerkey.xhtml" 
          media-type="application/xhtml+xml"/>    
    <item id="notes" 
          href="notes.xhtml" 
          media-type="application/xhtml+xml"/>
    <item id="cover" 
          href="./images/cover.svg" 
          properties="cover-image"
          media-type="image/svg+xml"/>
    <item id="f1" 
          href="./images/fig1.jpg" 
          media-type="image/jpeg"/>
    <item id="f2" 
          href="./images/fig2.jpg" 
          media-type="image/jpeg"/>
    <item id="css" 
          href="./style/book.css" 
          media-type="text/css"/>   
    <item id="pls" 
          href="./speech/dict.pls" 
          media-type="application/pls+xml"/>
</manifest>
Manifest Fallbacks

EPUB Creators MAY reference Foreign Resources in contexts in which an intrinsic fallback cannot be provided (e.g., directly from spine itemref elements; from [[HTML]] img, iframe and link elements in XHTML Content Documents; and from @import rules in CSS Style Sheets). EPUB Creators MUST provide manifest fallbacks in such cases.

The fallback attribute on the manifest item element specifies the fallback for the referenced Publication Resource. The fallback attribute's IDREF [[XML]] value MUST resolve to another item in the manifest. This fallback item MAY itself specify another fallback item, and so on.

The ordered list of all the ID references that a Reading System can reach, starting from a given item's fallback attribute, represents the fallback chain for that item. The order of the resources in the fallback chain represents the EPUB Creator's preferred fallback order.

Fallback chains MUST conform to one of the following requirements, as appropriate:

Fallback chains MUST NOT contain circular or self-references to item elements in the chain.

EPUB Creators MAY provide fallbacks for Top-Level Content Documents that are EPUB Content Documents (e.g., to provide fallbacks for scripted content).

As it is not possible to use manifest fallbacks for resources represented in data URLs, EPUB Creators can only represent Foreign Resources as data URLs where an intrinsic fallback mechanism is available.

The bindings Element (Deprecated)

The bindings element defines a set of custom handlers for media types not supported by this specification. Its use is deprecated.

Refer to [[EPUBPublications-301]] for more information about this element.

Spine Section
The spine Element

The spine element defines an ordered list of manifest item references that represent the default reading order.

Element name

spine

Usage

REQUIRED third child of package, following manifest.

Attributes
Content Model

itemref [1 or more]

The spine MUST specify at least one Publication Resource.

EPUB Creators MUST list in the spine all Publication Resources that are hyperlinked to from Publication Resources in the spine, where hyperlinking encompasses any linking mechanism that requires the user to navigate away from the current resource. Common hyperlinking mechanisms include the href attribute of the [[HTML]] a and area elements and scripted links (e.g., using DOM Events and/or form elements). The requirement to list hyperlinked resources applies recursively (i.e., EPUB Creators must list all Publication Resources hyperlinked from hyperlinked Publication Resources, and so on.).

EPUB Creators also MUST list in the spine all Publication Resources hyperlinked to from the EPUB Navigation Document, regardless of whether EPUB Creators include the Navigation Document in the spine.

As Remote Resources referenced from hyperlinks are not Publication Resources, they are not subject to the requirement to include in the spine (e.g., Web pages and resources).

Embedded Publication Resources (e.g., via the [[HTML]] iframe element) must not be listed in the spine.

The page-progression-direction attribute sets the global direction in which the content flows. Allowed values are ltr (left-to-right), rtl (right-to-left) and default. When EPUB Creators specify the default value, they are expressing no preference and the Reading System can choose the rendering direction.

Although the page-progression-direction attribute sets the global flow direction, individual Content Documents and parts of Content Documents MAY override this setting (e.g., via the writing-mode CSS property). Reading Systems can also provide mechanisms to override the default direction (e.g., buttons or settings that allow the application of alternate style sheets).

The legacy toc attribute takes an IDREF [[XML]] that identifies the manifest item that represents the NCX.

The itemref Element

The itemref element identifies a Publication Resource in the default reading order.

Element Name

itemref

Usage

As a child of spine. Repeatable.

Attributes
Content Model

Empty

Each itemref element MUST reference the ID [[XML]] of a unique item in the manifest via the IDREF [[XML]] in its idref attribute (i.e., two or more itemref elements cannot reference the same item).

Each referenced manifest item MUST be either a) an EPUB Content Document or b) another type of Publication Resource which, regardless of whether it is a Core Media Type Resource or a Foreign Resource, MUST include an EPUB Content Document in its fallback chain.

Although EPUB Publications require an EPUB Navigation Document, it is not mandatory to include it in the spine.

The linear attribute indicates whether the referenced item contains content that contributes to the primary reading order and that Reading Systems must read sequentially ("yes"), or auxiliary content that enhances or augments the primary content that Reading Systems can access out of sequence ("no"). Examples of auxiliary content include notes, descriptions, and answer keys.

The linear attribute allows Reading Systems to distinguish content that a user should access as part of the default reading order from supplementary content which a Reading System might, for example, present in a popup window or omit from an aural rendering.

Specifying that content is non-linear does not require Reading Systems to present it in a specific way, however; it is only a hint to the purpose. Reading Systems may present non-linear content where it occurs in the spine, for example, or may skip it until users reach the end of the spine.

EPUB Creators should list non-linear content at the end of the spine except when it makes sense for users to encounter it between linear spine items.

The spine MUST contain at least one linear itemref element — whose linear attribute value is either explicitly or implicitly set to "yes". Reading Systems will assume the value "yes" for itemref elements without a linear attribute.

EPUB Creators MUST provide a means of accessing all non-linear content (e.g., hyperlinks in the content or from the EPUB Navigation Document).

The Spine Properties Vocabulary is the default vocabulary for the properties attribute.

EPUB Creators MAY add terms from other vocabularies as defined in .

Examples
Collections
The collection Element

The collection element defines a related group of resources.

Element Name

collection

Usage

OPTIONAL sixth element of package. Repeatable.

Attributes
Content Model

In this order: metadata [0 or 1], ( collection [1 or more] or ( collection [0 or more], link [1 or more] ))

The collection element allows EPUB Creators to assemble resources into logical groups for a variety of potential uses: enabling reassembly into a meaningful unit of content split across multiple EPUB Content Documents (e.g., an index split across multiple documents), identifying resources for specialized purposes (e.g., preview content), or collecting together resources that present additional information about the EPUB Publication.

The collection element, as defined in this section, represents a generic framework from which specializations are intended to be derived (e.g., through EPUB sub-specifications). Such specializations MUST define the purpose of the collection element, as well as all requirements for its valid production and use (specifically any requirements that differ from the general framework presented below).

Each specialization MUST define a role value that uniquely identifies all conformant collection elements. EPUB Creators MUST identify the role of each collection element in its role attribute, whose value MUST be one or more NMTOKENs [[XMLSCHEMA-2]] and/or absolute-URL-with-fragment strings [[URL]].

This specification reserves the use of NMTOKEN values for roles defined in EPUB specifications. NMTOKEN values not defined by a recognized specification are not valid. This section does not define any roles.

Third parties MAY define custom roles for the collection element, but they MUST identify such roles using absolute-URL-with-fragment strings [[URL]]. Custom roles MUST NOT incorporate the string "idpf.org" in the host component [[URL]] of their identifying URL.

The former IDPF EPUB 3 Working Group maintained both a registry of role extensions and a list of custom extension roles. This Working Group no longer maintains these registries and does not anticipate defining new types of collections.

The OPTIONAL metadata element child of collection is an adaptation of the package metadata element, with the following differences in syntax and semantics:

EPUB specifications that implement collections MAY override package-level restrictions on the use of metadata elements.

A collection MAY define sub-collections through the inclusion of one or more child collection elements.

  • The rel attribute is OPTIONAL.

  • The properties attribute also accepts manifest item properties without a prefix (e.g., so that a collection can declare its own Navigation Document or cover image).

  • EPUB Creators MUST NOT specify the refines attribute.

Each link element MUST reference a resource that is a member of the group. The order of link elements is not significant.

Specializations of the collection element MAY tailor the requirements defined above to better reflect their needs (e.g., requiring metadata, imposing further restrictions on the use of elements and attributes, or making the order of link elements significant). However, the resulting content model MUST represent a valid subset of the one defined in this section (e.g., specializations cannot introduce new elements or attributes, or re-introduce those expressly forbidden above). Specializations MUST NOT define collections in a way that overrides the requirements of the manifest and spine.

The rendering of an EPUB Publication MUST NOT be dependent on the recognition of collection elements. The content MUST remain consumable by a user without any information loss or other significant deterioration.

Legacy Content
The meta Element

The meta element [[OPF-201]] is a legacy feature that previously provided a means of including generic metadata. The EPUB 3 meta element, which uses different attributes and requires text content, replaces this attribute.

For more information about the meta element, refer to its definition in [[OPF-201]].

The guide Element

The guide element [[OPF-201]] is a legacy feature that previously provided machine-processable navigation to key structures. The landmarks nav in the EPUB Navigation Document replaces this element.

For more information about the guide element, refer to its definition in [[OPF-201]].

NCX

The NCX [[OPF-201]] is a legacy feature that previously provided the table of contents. The EPUB Navigation Document replaces this document.

For more information about the NCX, refer to its definition in [[OPF-201]].

EPUB Content Documents

XHTML Content Documents

Introduction

This section defines a profile of [[HTML]] for creating XHTML Content Documents. An instance of an XML document that conforms to this profile is a Core Media Type Resource and is referred to in this specification as an XHTML Content Document.

XHTML Requirements

An XHTML Content Document:

  • MUST be an [[HTML]] document that conforms to the XHTML syntax.

  • MUST conform to the conformance criteria for all document constructs defined by [[HTML]] unless explicitly overridden in .

  • MAY include extensions to the [[HTML]] grammar as defined in , and MUST conform to all content conformance constraints defined therein.

Unless specified otherwise, XHTML Content Documents inherit all definitions of semantics, structure, and processing behaviors from the [[HTML]] specification.

The recommendation that EPUB Publications follow the accessibility requirements in [[EPUB-A11Y-11]] applies to XHTML Content Documents. See Accessibility.

HTML Extensions

This section defines EPUB 3 XHTML Content Document extensions to the underlying [[HTML]] document model.

Although [[HTML]] allows user agents to support vendor-neutral extensions, unless such extensions are listed in this section, they are not supported features of EPUB 3.

Structural Semantics

EPUB Creators MAY use the epub:type attribute in XHTML Content Documents to express structural semantics.

As the [[HTML]] head element contains metadata for the document, structural semantics expressed on this element or any descendant of it have no meaning.

RDFa

The [[HTML-RDFA]] specification defines a set of attributes that EPUB Creators MAY use in XHTML Content Documents to semantically enrich the content. The use of these attributes MUST conform to the requirements defined in [[HTML-RDFA]].

The [[HTML-RDFA]] specification defines changes to the [[HTML]] content model when authors use RDFa attributes. This modified content model is valid in XHTML Content Documents.

The listing of RDFa does not express a preference on the part of the Working Group, only that these attributes represent an extension of the HTML grammar. EPUB Creators can also specify microdata attributes [[HTML]] and linked data [[JSON-LD11]] in XHTML Content Documents as both are natively supported.

SSML Attributes
Introduction

The W3C Speech Synthesis Markup Language [[SSML]] is a language used for assisting Text-to-Speech (TTS) engines in generating synthetic speech. Although SSML is designed as a standalone document type, it also defines semantics suitable for use within other markup languages.

This specification recasts the [[SSML]] phoneme element as two attributes — ssml:ph and ssml:alphabet — and makes them available within XHTML Content Documents.

For more information on EPUB 3 features related to synthetic speech, refer to Text-to-speech [[EPUB-OVERVIEW-33]].

The ssml:ph attribute

The ssml:ph attribute specifies a phonemic/phonetic pronunciation of the text represented by its carrying element.

Attribute Name

ph

Namespace

https://www.w3.org/2001/10/synthesis

Usage

Global attribute. EPUB Creators MAY specify on all elements with which they can logically associate a phonetic equivalent (e.g., elements that contain textual information).

EPUB Creators MUST NOT specify the attribute on a descendant of an element that already carries this attribute.

Value

A phonemic/phonetic expression, syntactically valid with respect to the phonemic/phonetic alphabet used.

This attribute inherits all the semantics of the [[SSML]] phoneme element ph attribute, with the following addition:

  • When the ssml:ph attribute appears on an element that has text node descendants, the corresponding document text to which the pronunciation applies is the string that results from concatenating the descendant text nodes, in document order. The specified phonetic pronunciation MUST therefore logically match the element's textual data in its entirety (i.e., not just an isolated part of its content).

The ssml:alphabet attribute

The ssml:alphabet attribute specifies which phonemic/phonetic pronunciation alphabet is used in the value of the ssml:ph attribute.

Attribute Name

alphabet

Namespace

https://www.w3.org/2001/10/synthesis

Usage

Global attribute. EPUB Creators MAY specify on any element.

Value

The name of the pronunciation alphabet used in the value of ssml:ph (inherited).

This attribute inherits all the semantics of the [[SSML]] phoneme element alphabet attribute, with the following addition:

  • The value of the ssml:alphabet attribute is inherited in the document tree. The pronunciation alphabet used in a given ssml:ph attribute value is determined by locating the first occurrence of the ssml:alphabet attribute starting with the element on which the ssml:ph attribute appears, followed by the nearest ancestor element.

Although the [[SSML]] specification refers to a registry of alphabets, one has not been published. As the charter of the W3C Voice Browser Working Group has expired, the Working Group does not anticipate the publication of such a registry. EPUB Creators therefore should reference Reading System support documentation to determine what alphabet values they support. Some common alphabets include x-JEITA (also x-JEITA-IT-4002 and x-JEITA-IT-4006) and x-sampa.

Content Switching (Deprecated)

The switch element provides a simple mechanism through which EPUB Creators can tailor the content displayed to users, one that is not dependent on the scripting capabilities of the EPUB Reading System.

Use of the switch element is deprecated. Refer to its definition in [[EPUBContentDocs-301]] for usage information.

The epub:trigger Element (Deprecated)

The trigger element enables the creation of markup-defined user interfaces for controlling multimedia objects, such as audio and video playback, in both scripted and non-scripted contexts.

Use of the trigger element is deprecated. Refer to its definition in [[EPUBContentDocs-301]] for usage information.

HTML Deviations and Constraints

This section defines deviations from, and constraints on, the underlying [[HTML]] document model applicable to EPUB 3 XHTML Content Documents.

Embedded MathML

XHTML Content Documents support embedded [[MATHML3]]. Occurrences of MathML markup MUST conform to the constraints expressed in the MathML specification [[MATHML3]], with the following additional restrictions:

Presentation MathML

The math element MUST contain only Presentation MathML, except within the annotation-xml element.

Content MathML

EPUB Creators MAY include Content MathML within MathML markup in XHTML Content Documents, and, when present, MUST include it within an annotation-xml child element of a semantics element.

When EPUB Creators include Content MathML per the previous condition, they MUST set the given annotation-xml element's encoding attribute to either of the functionally-equivalent values MathML-Content or application/mathml-content+xml, and the name attribute to contentequiv.

Deprecated MathML

EPUB Creators MUST NOT include elements and attributes marked as deprecated in [[MATHML3]] within MathML markup in XHTML Content Documents.

This subset eases the implementation burden on Reading Systems and promotes accessibility, while retaining compatibility with [[HTML]] user agents.

The mathml property of the manifest item element indicates that an XHTML Content Document contains embedded MathML.

Embedded SVG

XHTML Content Documents support the embedding of SVG document fragments [[SVG]] by reference (embedding via reference, for example, from an img or object element) and by inclusion (embedding via direct inclusion of the svg element in the XHTML Content Document).

The content conformance constraints for SVG embedded in XHTML Content Documents are the same as defined for SVG Content Documents in .

The svg property of the manifest item element indicates that an XHTML Content Document contains embedded SVG.

Unicode Restrictions

This section lists restrictions on the Unicode character repertoire.

Private Use Characters and Embedded Fonts

Any included characters that map to a code point within one of the Private Use Area (PUA) ranges as defined in [[Unicode]] MUST occur within a string that is styled or attributed in a manner that includes a reference to an embedded font [[CSS-Fonts-3]] that contains an appropriate glyph for that code point.

Discouraged Constructs
The rp Element

The [[HTML]] rp element is intended to provide a fallback for older Reading Systems that do not recognize ruby markup (i.e., a parenthesis display around ruby markup). As EPUB 3 Reading Systems are ruby-aware, and can provide fallbacks, EPUB Creators should not use rp elements.

The embed Element

Since the [[HTML]] embed element does not include intrinsic facilities to provide fallback content for Reading Systems that do not support scripting, EPUB Creators are discouraged from using the element when the referenced resource includes scripting. The [[HTML]] object element is a better alternative, as it includes intrinsic fallback capabilities.

Foreign Resource Restrictions

EPUB Creators MAY reference Foreign Resources from elements that have intrinsic fallback mechanisms, where an intrinsic fallback method is the capability to offer an alternative presentation if Reading Systems do not support the foreign resource. For example, most [[HTML]] embedded content elements provide options for alternative rendering, such as allowing multiple sources to be specified or allowing embedded HTML content for when user agents cannot render a resource. When referencing a Foreign Resource, EPUB Creators MUST provide a Core Media Type Resource or embedded HTML content via the given element's intrinsic fallback mechanism.

EPUB Creators MAY embed [[HTML]] flow content within the audio and video elements for rendering in older Reading Systems that do not recognize these elements (e.g., EPUB 2 Reading Systems), but it does not represent a fallback Core Media Type Resource.

Due to the variety of sources that EPUB Creators can specify in the [[HTML]] img element, the following fallback conditions apply to its use:

  • If it is the child of a picture element:

    • it MUST reference Core Media Type Resources from its src and srcset attributes, when EPUB Creators specify those attributes; and
    • each sibling source element MUST reference a Core Media Type Resource from its src and srcset attributes unless it specifies a media type in its type attribute that is not a Core Media Type.
  • Otherwise, it MAY reference Foreign Resources in its src and srcset attributes provided EPUB Creators define a manifest fallback.

EPUB Creators MAY reference Foreign Resources from the following [[HTML]] elements without providing a fallback Core Media Type Resource:

Refer to manifest fallbacks for the provision of fallbacks for elements without intrinsic mechanisms, such as the [[HTML]] iframe.

SVG Content Documents

Reading Systems may not support all the features of [[SVG]] or supported them across all platforms that Reading Systems run on. When utilizing such features, EPUB Creators should consider the inherent risks on interoperability and document longevity.

Introduction

The Scalable Vector Graphics (SVG) specification [[SVG]] defines a format for representing final-form vector graphics and text.

Although EPUB Creators typically use XHTML Content Documents as the top-level document type, the use of SVG Content Documents is also permitted. EPUB Creators will typically only need SVGs for certain special cases, such as when final-form page images are the only suitable representation of the content (e.g., for cover art or in the context of manga or comic books).

This section defines a profile for [[SVG]] documents. An instance of an XML document that conforms to this profile is a Core Media Type Resource and is referred to in this specification as an SVG Content Document.

This section defines conformance requirements for SVG Content Documents. Refer to for the conformance requirements for SVG embedded in XHTML Content Documents.

SVG Requirements

An SVG Content Document:

The recommendation that EPUB Publications follow the accessibility requirements in [[EPUB-A11Y-11]] applies to SVG Content Documents. See Accessibility.

Restrictions on SVG

This specification restricts the content model of SVG Content Documents and SVG embedded in XHTML Content Documents as follows:

Cascading Style Sheets (CSS)

Introduction

CSS is an integral part of the Open Web Platform. Readers, publishers, and document authors expect CSS to "just work," as they expect HTML to just work.

In the past, EPUB defined a profile of CSS that mandated support for certain properties and provided prefixed versions of numerous other properties. Although the CSS Working Group no longer recommends the use of prefixed properties, this specification maintains some prefixed properties to avoid breaking existing content. But with the minor exceptions defined in this section, EPUB defers to the W3C to define CSS.

Keep in mind that some Reading Systems will not support all desired features of CSS. The following are known to be particularly problematic:

  • Reading System-induced pagination can interact poorly with style sheets as Reading Systems sometimes paginate using columns. This may result in incorrect values for viewport sizes. Fixed and absolute positioning are particularly problematic.

  • Some types of screens will render animations and transitions poorly (e.g., those with high latency).

CSS Requirements

A CSS style sheet:

  • MAY include any CSS properties, with the following exceptions:

  • MAY include the prefixed properties defined in .

  • MUST be encoded in UTF-8 or UTF-16 [[Unicode]], with UTF-8 as the RECOMMENDED encoding.

This specification restricts the use of the direction and unicode-bidi properties because Reading Systems may not implement, or may switch off, CSS processing. EPUB Creators must use the following format-specific methods when they need control over these aspects of the rendering:

Prefixed Properties

Earlier version of EPUB included prefixed CSS properties, as many CSS features related to world languages were not yet mature. To ensure backwards compatibility for content authored using these prefixes, they have been retained in this specification. Unless otherwise noted, prefixed properties and values behave exactly as their unprefixed equivalents as described in the appropriate CSS specification. The prefixed properties are documented in an Appendix.

EPUB Creators should use unprefixed properties and Reading Systems should support current CSS specifications. This specification retains the widely-used prefixed properties from [[EPUBContentDocs-301]], but removes support for the less-used ones. EPUB Creators should use CSS-native solutions for the removed properties whenever available.

The Working Group recommends that EPUB Creators currently using these prefixed properties move to unprefixed versions as soon as support allows, as the Working Group does not anticipate supporting them in the next major version of EPUB.

In some cases, the unprefixed versions of these properties now support additional values. Reading Systems MAY support these values even with the prefixed property.

Scripting

Script Inclusion

EPUB Content Documents MAY contain scripting using the facilities defined for this in the respective underlying specifications ([[HTML]] and [[SVG]]). When an EPUB Content Document contains scripting, this specification refers to it as a Scripted Content Document. This label also applies to XHTML Content Documents when they contain instances of [[HTML]] forms.

The scripted property of the manifest item element is used to indicate that an EPUB Content Document is a Scripted Content Document.

When an [[HTML]] script element contains a data block [[HTML]], it does not represent scripted content.

[[SVG]] does not define data blocks as of publication, but the same exclusion would apply if a future update adds the concept.

EPUB Creators should note that Reading Systems are required to behave as though a unique origin [[URL]] has been assigned to each EPUB Publication. In practice, this means that it is not possible for scripts to share data between EPUB Publications.

Which context a script is used in also determines the rights and restrictions that a Reading System places on it (refer to Scripting Conformance [[?EPUB-RS-33]] for more information).

Reading Systems may render Scripted Content Documents in a manner that disables other EPUB capabilities and/or provides a different rendering and user experience (e.g., by disabling pagination).

Scripting Contexts

EPUB 3 defines two contexts for script execution:

Whether EPUB Creators embed the code directly in the script element or reference it via the element's src attribute makes no difference to its executing context.

Which context EPUB Creators use for their scripts affects both what actions the scripts can perform and the likelihood of support in Reading Systems, as described in the following subsections.

Refer to for an example of the difference between the two contexts.

Container-Constrained Scripts

A container-constrained script is either of the following:

  • An instance of the [[HTML]] script element contained in an XHTML Content Document that is embedded in a parent XHTML Content Document using the [[HTML]] iframe element.

  • An instance of the [[SVG]] script element contained in an SVG Content Document that is embedded in a parent XHTML Content Document using the [[HTML]] iframe element.

A container-constrained script MUST NOT contain instructions for modifying the DOM of the EPUB Content Document that embeds it (i.e., the one that contains the iframe element). It also MUST NOT contain instructions for manipulating the size of its containing rectangle.

EPUB Creators should note that support for container-constrained scripting in Reading Systems is only recommended in reflowable documents [[EPUB-RS-33]]. Furthermore, Reading System support in fixed-layouts EPUBs is optional.

EPUB Creators should ensure container-constrained scripts degrade gracefully in Reading Systems without scripting support (see ).

EPUB Creators choosing to restrict the usage of scripting to the container-constrained model will ensure a more consistent user experience between scripted and non-scripted content (e.g., consistent pagination behavior).

Spine-Level Scripts

A spine-level script is an instance of the [[HTML]] script or [[SVG]] script element contained in a Top-level Content Document.

EPUB Creators should note that support for spine-level scripting in Reading Systems is only recommended in fixed-layout documents and reflowable documents set to scroll [[EPUB-RS-33]]. Furthermore, Reading System support in all other contexts is optional.

Top-level Content Documents that include spine-level scripting SHOULD remain consumable by the user without any information loss or other significant deterioration when scripting is disabled or not available (e.g., by employing progressive enhancement techniques or fallbacks). Failing to account for non-scripted environments in Top-level Content Documents can result in EPUB Publications being unreadable.

Event Model

EPUB Creators should consider the wide variety of possible Reading System implementations when adding scripting functionality to their EPUB Publications (e.g., not all devices have physical keyboards, and in many cases a soft keyboard is activated only for text input elements). Consequently, EPUB Creators should not rely on keyboard events alone; they should always provide alternative ways to trigger a desired action.

Scripting Accessibility

EPUB Content Documents that contain scripting SHOULD employ relevant [[WAI-ARIA]] accessibility techniques to ensure that the content remains consumable by all users.

Scripting Fallbacks

EPUB Content Documents that contain scripting MAY provide fallbacks for such content, either by using intrinsic fallback mechanisms (such as those available for the [[HTML]] object and canvas elements) or, when an intrinsic fallback is not applicable, by using a manifest-level fallback.

EPUB Creators MUST ensure that scripts only generate Core Media Type Resources or fragments thereof.

Pronunciation Lexicons

The W3C Pronunciation Lexicon Specification (PLS) [[PRONUNCIATION-LEXICON]] defines syntax and semantics for XML-based pronunciation lexicons to be used by Automatic Speech Recognition and Text-to-Speech (TTS) engines.

EPUB Creators MAY associate zero or more PLS Documents with an XHTML Content Document.

To associate a PLS Document with an XHTML Content Document, EPUB Creators MUST use the [[HTML]] link element with its rel attribute set to "pronunciation" and its type attribute set to the media type "application/pls+xml".

EPUB Creators SHOULD specify the link element hreflang attribute on each link, and its value MUST match the language for which the pronunciation lexicon is relevant [[PRONUNCIATION-LEXICON]] when specified.

PLS Documents MUST be valid to the RELAX NG schema available at the URL https://www.w3.org/TR/2008/REC-pronunciation-lexicon-20081014/pls.rng [[PRONUNCIATION-LEXICON]].

PLS Documents SHOULD use the file extension .pls.

For more information on EPUB 3 features related to synthetic speech, refer to Text-to-speech [[EPUB-OVERVIEW-33]].

EPUB Navigation Document

Introduction

The EPUB Navigation Document is a mandatory component of an EPUB Publication. It allows EPUB Creators to include a human- and machine-readable global navigation layer, thereby ensuring increased usability and accessibility for the user.

The EPUB Navigation Document is a special type of XHTML Content Document that defines the table of contents for Reading Systems. It may also include other specialized navigation elements, such as a page list and a list of key landmarks. These navigation elements have additional restrictions on their content to facilitate their processing.

The EPUB Navigation Document is not exclusively for machine processing, however. There are no restrictions on the structure or content of the EPUB Navigation Document outside of the specialized navigation elements (i.e., EPUB Creators can mark the rest of the document up like any other XHTML Content Document). As a result, it can also be part of the linear reading order, avoiding the need for duplicate tables of contents. EPUB Creators can hide navigation elements that are only for machine processing (e.g., the page list) with the hidden attribute.

Note that Reading Systems may strip scripting, styling, and HTML formatting as they generate navigational interfaces from information found in the EPUB Navigation Document. If EPUB Creators require such formatting and functionality, then they should also include the EPUB Navigation Document in the spine. The use of progressive enhancement techniques for scripting and styling of the navigation document will help ensure the content will retain its integrity when rendered in a non-browser context.

EPUB Navigation Document Definition

The nav Element: Restrictions

When a nav element carries the epub:type attribute in an EPUB Navigation Document, this specification restricts the content model of the element and its descendants as follows:

Content Model
nav

In this order:

ol

In this order:

  • li [1 or more]

li

In this order:

  • (span or a) [exactly 1]

  • ol [conditionally required]

span and a

In any order:

Note that there are no restrictions on the attributes allowed on these elements.

Refer the definition below for additional requirements.

The following elaboration of the content model of the nav element explains the purpose and restrictions of the various elements:

  • The ol child of the nav element represents the primary level of content navigation.

  • Each list item of the ordered list represents a heading, structure, or other item of interest. A child a element describes the target that the link points to, while a span element serves as a heading for breaking down lists into distinct groups (for example, an EPUB Creator could segment a large list of illustrations into several lists, one for each chapter).

  • The child a or span element MUST provide a non-zero-length text label after concatenation of all child content and application of white space normalization rules. When determining compliance with this requirement, the concatenated label MUST include text content contained in title or alt attributes for non-textual descendant elements.

  • If an a or span element contains instances of HTML embedded content that do not provide intrinsic text alternatives, the element MUST also contain a title attribute with an alternate text rendering of the link label.

  • The URL [[URL]] reference provided in the href attribute of the a element:

  • An ol (ordered list) element representing a subsidiary content level (e.g., all the subsection headings of a section) MAY follow an a element.

  • An ol (ordered list) element MUST follow a span element (span elements cannot occur in "leaf" li elements).

  • Regardless of whether an a or span element precedes it, every sublist MUST adhere to the content requirements defined in this section for constructing the primary navigation list.

As a conforming XHTML Content Document, EPUB Creators MAY include the EPUB Navigation Document in the spine.

In the context of this specification, the default display style of list items within nav elements is equivalent to the list-style: none property [[CSSSnapshot]]. EPUB Creators MAY specify alternative list styling using CSS for rendering of the document in the spine.

The nav Element: Types

Introduction

The nav elements defined in an EPUB Navigation Document are distinguished semantically by the value of their epub:type attribute.

This specification defines three types of navigation aid:

toc

Identifies the nav element that contains the table of contents. The toc nav is the only navigation aid that EPUB Creators must include in the EPUB Navigation Document.

page-list

Identifies the nav element that contains a list of pages for a print or other statically paginated source.

landmarks

Identifies the nav element that contains a list of points of interest.

An EPUB Navigation Document may contain at most one navigation aid for each of these types.

The EPUB Navigation Document may include additional navigation types. See for more information.

The toc nav Element

The toc nav element defines the primary navigational hierarchy. It conceptually corresponds to a table of contents in a printed work (i.e., it provides navigation to the major structural sections of the publication).

EPUB Creators SHOULD order the references in the toc nav element such that they reflect both:

The toc nav element MUST occur exactly once in an EPUB Navigation Document.

The page-list nav Element

The page-list nav element provides navigation to positions in the content that correspond to the locations of page boundaries present in a print source.

The page-list nav element is OPTIONAL in EPUB Navigation Documents and MUST NOT occur more than once.

The page-list nav element SHOULD contain only a single ol descendant (i.e., no nested sublists).

EPUB Creators MAY identify the destinations of the page-list references in their respective EPUB Content Documents using the pagebreak term.

The landmarks nav Element

The landmarks nav element identifies fundamental structural components in the content to enable Reading Systems to provide the user efficient access to them.

The epub:type attribute is REQUIRED on a element descendants of the landmarks nav element. The structural semantics of each link target within the landmarks nav element is determined by the value of this attribute.

The landmarks nav MUST NOT include multiple entries with the same epub:type value that reference the same resource, or fragment thereof.

The landmarks nav element is OPTIONAL in EPUB Navigation Documents and MUST NOT occur more than once.

Other nav Elements

EPUB Navigation Documents MAY contain one or more nav elements in addition to the toc, page-list, and landmarks nav elements defined in the preceding sections. If these nav elements are intended for Reading System processing, they MUST have an epub:type attribute and are subject to the content model restrictions defined in .

This specification imposes no restrictions on the semantics of any additional nav elements: they MAY represent navigational semantics for any information domain, and they MAY contain link targets with homogeneous or heterogeneous semantics.

The hidden attribute

In some cases, EPUB Creators might wish to hide parts of the navigation data within the content flow (i.e., the Reading System's principal rendering of the spine contents). A typical example is the list of page breaks, which EPUB Creators do not want Reading Systems to render as part of the content flow.

While the display property [[CSSSnapshot]] controls the visual rendering of EPUB Navigation Documents in Reading Systems with Viewports, not all Reading Systems provide such an interface. To control rendering across all Reading Systems, EPUB Creators MUST use the [[HTML]] hidden attribute to indicate which (if any) portions of the navigation data are excluded from rendering in the content flow. The hidden attribute has no effect on how Reading Systems render the navigation data outside of the content flow (such as in dedicated navigation user interfaces provided by Reading Systems).

Fixed Layouts

Introduction

EPUB documents, unlike print books or PDF files, are designed to change. The content flows, or reflows, to fit the screen and to fit the needs of the user. As noted in Rendering and CSS "content presentation adapts to the user, rather than the user having to adapt to a particular presentation of content." [[EPUB-OVERVIEW-33]]

But this principle does not work for all types of documents. Sometimes content and design are so intertwined it is not possible to separate them. Any change in appearance risks changing the meaning or losing all meaning. Fixed-Layout Documents give EPUB Creators greater control over presentation when a reflowable EPUB is not suitable for the content.

EPUB Creators define fixed layouts using a set of Package Document properties to control the rendering in Reading Systems. In addition, they set the dimensions of each Fixed-Layout Document in its respective EPUB Content Document.

EPUB 3 affords multiple mechanisms for representing fixed-layout content. When fixed-layout content is necessary, the EPUB Creator's choice of mechanism will depend on many factors including desired degree of precision, file size, accessibility, etc. This section does not attempt to dictate the EPUB Creator's choice of mechanism.

Fixed-Layout Package Settings

Layout

The rendition:layout property specifies whether the content is reflowable or pre-paginated.

When the rendition:layout property is specified on a meta element, it indicates that the paginated or reflowable layout style applies globally (i.e., for all spine items).

EPUB Creators MAY use the following values with the rendition:layout property:

reflowable

The content is not pre-paginated (i.e., Reading Systems apply dynamic pagination when rendering). Default value.

pre-paginated

The content is pre-paginated (i.e., Reading Systems produce exactly one page per spine itemref when rendering).

Reading Systems typically restrict or deny the application of user or user agent style sheets to pre-paginated documents because dynamic style changes are likely to have unintended consequence on the intrinsic properties of such documents. EPUB Creators should consider the negative impact on usability and accessibility that these restrictions have when choosing to use pre-paginated instead of reflowable content. Refer to Guideline 1.4 - Provide text configuration [[UAAG20]] for related information.

When the property is set to pre-paginated for a spine item, its content dimensions MUST be set as defined in .

The rendition:layout property MUST NOT be declared more than once.

Layout Overrides

EPUB Creators MAY specify the following properties locally on spine itemref elements to override the global value for the given spine item:

layout-pre-paginated
Specifies that the given spine item is pre-paginated.
layout-reflowable
Specifies that the given spine item is reflowable.

EPUB Creators MAY use only one of these overrides on any given spine item.

Orientation

The rendition:orientation property specifies which orientation the EPUB Creator intends the content to be rendered in.

When the rendition:orientation property is specified on a meta element, it indicates that the intended orientation applies globally (i.e., for all spine items).

EPUB Creators MAY use the following values with the rendition:orientation property:

landscape

Reading Systems should render the content in landscape orientation.

portrait

Reading Systems should render the content in portrait orientation.

auto

The content is not orientation constrained. Default value.

EPUB Creators MUST NOT declare the rendition:orientation property more than once.

Orientation Overrides

EPUB Creators MAY specify the following properties locally on spine itemref elements to override the global value for the given spine item:

orientation-auto
Specifies that the Reading System determines the orientation to render the spine item in.
orientation-landscape
Specifies that Reading Systems should render the given spine item in landscape orientation.
orientation-portrait
Specifies that Reading Systems should render the given spine item in portrait orientation.

EPUB Creators MAY use only one of these overrides on any given spine item.

Synthetic Spreads

The rendition:spread property specifies the intended Reading System synthetic spread behavior.

When the rendition:spread property is specified on a meta element, it indicates that the intended Synthetic Spread behavior applies globally (i.e., for all spine items).

EPUB Creators MAY use the following values with the rendition:spread property:

none

Do not incorporate spine items in a Synthetic Spread.

landscape

Render a Synthetic Spread for spine items only when the device is in landscape orientation.

portrait (deprecated)

The use of spreads only in portrait orientation is deprecated.

EPUB Creators should use the value "both" instead, as spreads that are readable in portrait orientation are also readable in landscape.

both

Render a Synthetic Spread regardless of device orientation.

auto

The EPUB Creator is not defining an explicit Synthetic Spread behavior. Default value.

The rendition:spread property MUST NOT be declared more than once.

When Synthetic Spreads are used in the context of HTML and SVG Content Documents, the dimensions given via the viewport meta element and viewBox attribute represents the size of one page in the spread, respectively.

Refer to spine for information about declaration of global flow directionality using the page-progression-direction attribute and that of local page-progression-direction within content documents.

Synthetic Spread Overrides

EPUB Creators MAY specify the following properties locally on spine itemref elements to override the global value for the given spine item:

spread-auto
Specifies the Reading System determines when to render a synthetic spread for the spine item.
spread-both
Specifies the Reading System should render a synthetic spread for the spine item in both portrait and landscape orientations.
spread-landscape
Specifies the Reading System should render a synthetic spread for the spine item only when in landscape orientation.
spread-none
Specifies the Reading System should not render a synthetic spread for the spine item.
spread-portrait
The spread-portrait property is deprecated. Refer to its definition in [[EPUBPublications-301]] for more information.

EPUB Creators MAY use only one of these overrides on any given spine item.

Spread Placement

When a Reading System renders a Synthetic Spread, the default behavior is to populate the spread by rendering the next EPUB Content Document in the next available unpopulated viewport, where the next available viewport is determined by the given page progression direction or by local declarations within Content Documents. An EPUB Creator MAY override this automatic population behavior and force Reading Systems to place a document in a particular viewport by specifying one of the following properties on its spine itemref element:

rendition:page-spread-center
The rendition:page-spread-center property specifies the forced placement of a Content Document in a Synthetic Spread.
rendition:page-spread-left
The rendition:page-spread-left property is an alias for the page-spread-left property.
rendition:page-spread-right
The rendition:page-spread-right property is an alias for the page-spread-right property.

The rendition:page-spread-left property indicates that the given spine item is to be rendered in the left-hand slot in the spread, and rendition:page-spread-right that it be rendered in the right-hand slot. The rendition:page-spread-center property indicates to override the synthetic spread mode and render a single viewport positioned at the center of the screen.

The rendition:page-spread-left, rendition:page-spread-right and rendition:page-spread-center properties apply to both pre-paginated and reflowable content, and they only apply when the Reading System is creating Synthetic Spreads.

Although EPUB Creators often indicate to use a spread in certain device orientations, the content itself does not represent true spreads (i.e., two consecutive pages that Reading Systems must rendered side-by-side for readability, such as a two-page map). To indicate that two consecutive pages represent a true spread, EPUB Creators SHOULD use the rendition:page-spread-left and rendition:page-spread-right properties on the spine items for the two adjacent EPUB Content Documents, and omit the properties on spine items where one-up or two-up presentation is equally acceptable.

EPUB Creators MAY only declare one page-spread-* property on any given spine item.

The rendition:page-spread-left and rendition:page-spread-right properties are aliases for the page-spread-left and spread-right properties. They allow the use of a single vocabulary for all fixed-layout properties. EPUB Creators can use either property set, but older Reading Systems might only recognize the unprefixed versions. The Working Group is not going to extend the EPUB Spine Properties Vocabulary to add an unprefixed page-spread-center property.

Viewport Dimensions (Deprecated)

The rendition:viewport property allows EPUB Creators to express the CSS initial containing block (ICB) [[CSS2]] for XHTML and SVG Content Documents whose rendition:layout property has been set to pre-paginated.

Use of the property is deprecated. Refer to its definition in [[EPUBPublications-301]] for more information.

Content Document Dimensions

This section defines rules for the expression and interpretation of dimensional properties of Fixed-Layout Documents.

Fixed-Layout Documents specify their initial containing block [[CSS2]] in the manner applicable to their format:

Expressing in XHTML

For XHTML Fixed-Layout Documents, the initial containing block [[CSS2]] dimensions MUST be expressed in a viewport meta tag using the syntax defined in [[CSS-Device-Adapt-1]].

Expressing in SVG

For SVG Fixed-Layout Documents, the initial containing block [[CSS2]] dimensions MUST be expressed using the viewBox attribute [[SVG]].

Open Container Format

OCF Abstract Container

Introduction

The OCF Abstract Container file system model uses a single common Root Directory for all the contents. All Local Resources for the EPUB Publication are located within the directory tree headed by the Root Directory, but no specific file system structure for them is mandated by this specification.

The file system model also includes a mandatory directory named META-INF that is a direct child of the Root Directory and stores the following special files:

container.xml [required]

Identifies the Package Document(s) that define the EPUB Publication.

signatures.xml [optional]

Contains digital signatures for various assets.

encryption.xml [optional]

Contains information about the encryption of Publication Resources. This file is mandatory when EPUB Creators use obfuscation.

metadata.xml [optional]

Used to store metadata about the OCF ZIP Container.

rights.xml [optional]

Used to store information about digital rights.

manifest.xml [optional]

A manifest of container contents as allowed by Open Document Format [[ODF]].

Refer to for conformance requirements for the various files in the META-INF directory.

File and Directory Structure

The virtual file system for the OCF Abstract Container MUST have a single common Root Directory for all the contents of the container.

The OCF Abstract Container MUST include a directory for configuration files named META-INF that is a direct child of the container's Root Directory. Refer to for the requirements for the contents of this directory.

The file name mimetype in the Root Directory is reserved for use by OCF ZIP Containers, as explained in .

EPUB Creators MAY locate all other files within the OCF Abstract Container in any location descendant from the Root Directory, provided they are not within the META-INF directory. EPUB Creators MUST NOT reference files in the META-INF directory from an EPUB Publication.

Relative URLs for Referencing Other Components

Files within the OCF Abstract Container MUST reference each other via relative-URL-with-fragment strings [[URL]].

The relevant language specification for a given file format determines the base URL [[URL]] used to parse relative-URL-with-fragment strings [[URL]]. For example, CSS defines how relative URL references work in the context of CSS style sheets and property declarations [[CSSSnapshot]].

Some language specifications reference Requests For Comments that preceded [[URL]], in which case the earlier RFC applies for content in that language.

Unlike most language specifications, the base URL [[URL]] for all files within the META-INF directory is the Root Directory of the OCF Abstract Container.

For example, if META-INF/container.xml has the following content:

<?xml version="1.0"?>
<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
    <rootfiles>
        <rootfile full-path="EPUB/Great_Expectations.opf"
            media-type="application/oebps-package+xml" />	
    </rootfiles>
</container>
            

then the path EPUB/Great_Expectations.opf is relative to the root directory for the OCF Abstract Container and not relative to the META-INF directory.

All relative-URL-with-fragment strings [[URL]] MUST, after parsing to URL records [[URL]], identify resources within the OCF Abstract Container (i.e., at or below the Root Directory).

Path and File Names

In the context of the Abstract Container, Path Names and File Names are case sensitive.

In addition, the following restrictions are designed to allow Path Names and File Names to be used without modification on most operating systems:

  • Path and File Names MUST be UTF-8 [[Unicode]] encoded.

  • File Names MUST NOT exceed 255 bytes.

  • The Path Name for any directory or file within the OCF Abstract Container MUST NOT exceed 65535 bytes.

  • File Names MUST NOT use the following [[Unicode]] characters, as commonly used operating systems may not support these characters consistently:

    • SOLIDUS: / (U+002F)

    • QUOTATION MARK: " (U+0022)

    • ASTERISK: * (U+002A)

    • FULL STOP as the last character: . (U+002E)

    • COLON: : (U+003A)

    • LESS-THAN SIGN: < (U+003C)

    • GREATER-THAN SIGN: > (U+003E)

    • QUESTION MARK: ? (U+003F)

    • REVERSE SOLIDUS: \ (U+005C)

    • VERTICAL LINE: | (U+007C)

    • DEL (U+007F)

    • C0 range (U+0000 … U+001F)

    • C1 range (U+0080 … U+009F)

    • Private Use Area (U+E000 … U+F8FF)

    • All Unicode Non Characters, specifically:

      • The 32 contiguous characters in the Basic Multilingual Plane (U+FDD0 … U+FDEF)

      • The last two code points of the Basic Multilingual Plane (U+FFFE and U+FFFF)

      • The last two code points at the end of the Supplementary Planes (U+1FFFE, U+1FFFF … U+EFFFE, U+EFFFF)

    • Specials (U+FFF0 … U+FFFF)

    • Tags and Variation Selectors Supplement (U+E0000 … U+E0FFF)

    • Supplementary Private Use Area-A (U+F0000 … U+FFFFF)

    • Supplementary Private Use Area-B (U+100000 … U+10FFFF)

  • All File Names within the same directory MUST be unique following full case folding [[Unicode]] and NFC normalization [[TR15]]. (Refer to Unicode Canonical Case Fold Normalization Step [[?CHARMOD-NORM]] for more information.)

Some commercial ZIP tools do not support the full Unicode range for File Names. EPUB Creators who want to use ZIP tools that have these restrictions may find it best to restrict their File Names to the [[US-ASCII]] range.

META-INF Directory

Inclusion

All OCF Abstract Containers MUST include a directory called META-INF in their Root Directory.

This directory is reserved for configuration files, specifically those defined in .

Reserved Files
Container File (container.xml)

The REQUIRED container.xml file in the META-INF directory identifies the Package Documents available in the OCF Abstract Container.

All [[XML]] elements defined in this section are in the urn:oasis:names:tc:opendocument:xmlns:container namespace [[XML-NAMES]] unless specified otherwise.

The contents of this file MUST be valid to the definition in this section after removing all elements and attributes from other namespaces (including all attributes and contents of such elements).

An XML Schema also informally defines the content of this file.

The container Element

The container element is the root element of the container.xml file.

Element Name

container

Usage

Root element of the container.xml file.

Attributes
version [required]
This attribute MUST have the value "1.0".
Content Model

In this order:

The rootfiles Element

The rootfiles element contains a list of Package Documents available in the EPUB Container.

Element Name

rootfiles

Usage

REQUIRED first child of container.

Attributes

None

Content Model
The rootfile Element

Each rootfile element identifies the location of one Package Document in the EPUB Container.

Element Name

rootfile

Usage

As child of the rootfiles element. Repeatable.

Attributes
full-path [required]

Identifies the location of a Package Document.

The value of the attribute MUST be a path-relative-scheme-less-URL string [[URL]]. The path is relative to the Root Directory.

media-type [required]

Identifies the media type of the Package Document.

The value of the attribute MUST be "application/oebps-package+xml".

Content Model

Empty

If an EPUB Creator defines more than one rootfile element, each MUST reference a Package Document that conforms to the same version of EPUB. Each Package Document represents one rendering of the EPUB Publication.

Although the EPUB Container provides the ability to reference more than one Package Document, this specification does not define how to interpret, or select from, the available options. Refer to [[EPUB-MULTI-REND-11]] for more information on how to bundle more than one rendering of the content.

Container Example

The following example shows a sample container.xml file for an EPUB Publication with the root file EPUB/My Crazy Life.opf (the Package Document):

<?xml version="1.0"?>
<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
    <rootfiles>
        <rootfile full-path="EPUB/My_Crazy_Life.opf"
            media-type="application/oebps-package+xml" />
    </rootfiles>
</container>
                    
Encryption File (encryption.xml)

The OPTIONAL encryption.xml file in the META-INF directory holds all encryption information on the contents of the container. If an EPUB Creator encrypts any resources within the container, they MUST include an encryption.xml file to provide information about the encryption used.

The encryption element
Element Name

encryption

Namespace

urn:oasis:names:tc:opendocument:xmlns:container

Usage

Root element of the encryption.xml file.

Attributes

None

Content Model

In any order:

  • EncryptedKey [1 or more]
  • EncryptedData [1 or more]

The encryption element contains child elements of type EncryptedKey and EncryptedData as defined by [[XMLENC-CORE1]].

An EncryptedKey element describes each encryption key used in the container, while an EncryptedData element describes each encrypted file. Each EncryptedData element refers to an EncryptedKey element, as described in XML Encryption.

An XML Schema also informally defines the content of the encryption.xml file.

OCF encrypts individual files independently, trading off some security for improved performance, allowing the container contents to be incrementally decrypted. Encryption in this way exposes the directory structure and file naming of the whole package.

OCF uses XML Encryption [[XMLENC-CORE1]] to provide a framework for encryption, allowing a variety of algorithms to be used. XML Encryption specifies a process for encrypting arbitrary data and representing the result in XML. Even though an OCF Abstract Container may contain non-XML data, EPUB Creators can use XML Encryption to encrypt all data in an OCF Abstract Container. OCF encryption supports only the encryption of entire files within the container, not parts of files. EPUB Creators MUST NOT encrypt the encryption.xml file when present.

Encrypted data replaces unencrypted data in an OCF Abstract Container. For example, if an EPUB Creator encrypts an image named photo.jpeg, they should replace the contents of the photo.jpeg resource with its encrypted contents. Within the ZIP directory, EPUB Creators SHOULD store encrypted files rather than Deflate-compress them.

Note that some situations require obfuscating the storage of embedded resources referenced by an EPUB Publication to make them more difficult to extract for unrestricted use (e.g., fonts). Although obfuscation is not encryption, Reading Systems use the encryption.xml file in conjunction with the resource obfuscation algorithm to identify resources to de-obfuscated.

EPUB Creators MUST NOT encrypt or obfuscate the following files:

  • mimetype
  • META-INF/container.xml
  • META-INF/encryption.xml
  • META-INF/manifest.xml
  • META-INF/metadata.xml
  • META-INF/rights.xml
  • META-INF/signatures.xml
  • Package Document

EPUB Creators MAY subsequently encrypt signed resources using the Decryption Transform for XML Signature [[XMLENC-DECRYPT]]. This feature enables a Reading System to distinguish data encrypted before signing from data encrypted after signing.

Order of Compression and Encryption

When stored in a ZIP container, EPUB Creators SHOULD compress streams of data with Non-Codec content types before encrypting them. EPUB Creators MUST use Deflate compression. This practice ensures that file entries stored in the ZIP container have a smaller size.

EPUB Creators SHOULD NOT compress streams of data with Codec content types before encrypting them. In such cases, additional compression introduces unnecessary processing overhead at production time (especially with large resource files) and impacts audio/video playback performance at consumption time. In some cases, the combination of compression with some encryption schemes might even compromise the ability of Reading Systems to handle partial content requests (e.g. HTTP byte ranges), due to the technical impossibility to determine the length of the full resource ahead of media playback (e.g. HTTP Content-Length header).

When EPUB Creators compress streams of data before encrypting, they SHOULD provide additional EncryptionProperties metadata to specify the size of the initial resource (i.e., before compression and encryption), as per the Compression XML element defined below. When EPUB Creators do not compress streams of data before encrypting, they MAY provide the additional EncryptionProperties metadata to specify the size of the initial resource (i.e., before encryption).

Element Name

Compression

Namespace

http://www.idpf.org/2016/encryption#compression

Usage

OPTIONAL child of EncryptionProperty.

Attributes
Method [required]

Identifies the compression method used.

Value is either "0" (no compression) or "8" (Deflate algorithm).

OriginalLength [required]

Represents the size of the initial resource (number of bytes).

Value is a positive integer.

Content Model

Empty

Manifest File (manifest.xml)

The OPTIONAL manifest.xml file in the META-INF directory provides a manifest of files in the Container.

The OCF specification does not mandate a format for the manifest.

Note that Package Documents specify the only manifests used for processing EPUB Publications. Reading Systems do not use this file.

This feature exists only for compatibility with [[ODF]].
Metadata File (metadata.xml)

EPUB Creators MUST use the OPTIONAL metadata.xml file in the META-INF directory only for container-level metadata.

If EPUB Creators include a metadata.xml file, they SHOULD use only namespace-qualified elements [[XML-NAMES]] in it. The file SHOULD contain the root element metadata in the namespace http://www.idpf.org/2013/metadata, but this specification allows other root elements for backwards compatibility.

This version of the specification does not define metadata for use in the metadata.xml file. Future versions of this specification MAY define container-level metadata.

Rights Management File (rights.xml)

This specification resrves the OPTIONAL rights.xml file in the META-INF directory for digital rights management (DRM) information for trusted exchange of EPUB Publications among rights holders, intermediaries, and users.

This version of the specification does not require a specific format for DRM information, but a future version might. EPUB Creators SHOULD only use namespace-qualified elements [[XML-NAMES]] in the rights.xml file to avoid collision with a future format.

When EPUB Creators do not include a rights.xml file, no part of the container is rights governed at the container level. Rights expressions might exist within the EPUB Publications.

If EPUB Creators do not include a rights.xml file, no part of the OCF Abstract Container is rights governed.

Digital Signatures File (signatures.xml)

Adding a digital signature is not a guarantee that a malicious actor cannot tamper with an EPUB Publication as Reading Systems do not have to check signatures.

The OPTIONAL signatures.xml file in the META-INF directory holds digital signatures for the container and its contents.

The signatures element
Element Name

signatures

Namespace

urn:oasis:names:tc:opendocument:xmlns:container

Usage

Root element of the signature.xml file.

Attributes

None

Content Model
  • Signature [1 or more]

The signature element contains child elements of type Signature, as defined by [[XMLDSIG-CORE1]]. EPUB Creators can apply signatures to an EPUB Publication as a whole or to its parts, and can specify the signing of any kind of data (i.e., not just XML).

An XML Schema also informally defines the content of the signatures.xml file.

When an EPUB Creator does not include a signatures.xml file, they are not signing any part of the container at the container level. Digital signing might exist within the EPUB Publication.

When an EPUB Creator creates a data signature for the container, they SHOULD add the signature as the last child Signature element of the signatures element.

Each Signature in the signatures.xml file identifies by URL [[URL]] the data to which the signature applies, using the [[XMLDSIG-CORE1]] Manifest element and its Reference sub-elements. EPUB Creator may sign individual container files separately or together. Separately signing each file creates a digest value for the resource that Reading Systems can validate independently. This approach might make a Signature element larger. If EPUB Creators sign files together, they can list the set of signed files in a single XML Signature Manifest element and reference them by one or more Signature elements.

EPUB Creators can sign any or all files in the container in their entirety, except for the signatures.xml file since that file will contain the computed signature information. Whether and how EPUB Creators sign the signatures.xml file depends on their objective.

If the EPUB Creator wants to allow signatures to be added or removed from the container without invalidating their signature, they SHOULD NOT sign the signatures.xml file.

If the EPUB Creator wants any addition or removal of a signature to invalidate their signature, they can use the Enveloped Signature transform defined in Section 6.6.4 of [[XMLDSIG-CORE1]] to sign the entire preexisting signature file excluding the Signature being created. This transform would sign all previous signatures, and it would become invalid if a subsequent signature were added to the package.

If the EPUB Creator wants the removal of an existing signature to invalidate the their signature, but also wants to allow the addition of signatures, they could use an XPath transform to sign just the existing signatures. The details of such a transform are outside the scope of this specification, however.

The [[XMLDSIG-CORE1]] specification does not associate any semantics with a signature; an agent might include semantic information, for example, by adding information to the Signature element that describes the signature. The [[XMLDSIG-CORE1]] specification describes how additional information can be added to a signature, such as by use the SignatureProperties element.

OCF ZIP Container

Introduction

An OCF ZIP Container is a physical single-file manifestation of an OCF Abstract Container. The Container allows:

  • the exchange of in-progress EPUB Publication between different individuals and/or different organizations;

  • the transfer of EPUB Publications from a publisher or conversion house to the distribution or sales channel; and

  • the delivery of EPUB Publications to EPUB Reading Systems or users.

ZIP File Requirements

An OCF ZIP Container uses the ZIP format as specified by [[ZIP]], but with the following constraints and clarifications:

  • The contents of the OCF ZIP Container MUST be a conforming OCF Abstract Container.

  • OCF ZIP Containers MUST NOT use the features in the ZIP application note [[ZIP]] that allow ZIP files to be spanned across multiple storage media or be split into multiple files.

  • OCF ZIP Containers MUST include only stored (uncompressed) and Deflate-compressed ZIP entries within the ZIP archive.

  • OCF ZIP Containers MAY use the ZIP64 extensions defined as "Version 1" in section V, subsection G of the application note [[ZIP]] and SHOULD use only those extensions when the content requires them.

  • OCF ZIP Containers MUST NOT use the encryption features defined by the ZIP format; instead, encryption MUST be done using the features described in .

  • OCF ZIP Containers MUST encode File System Names using UTF-8 [[Unicode]].

The following constraints apply to specific fields in the OCF ZIP Container archive:

  • In the local file header table, EPUB Creators MUST set the version needed to extract fields to the values 10, 20 or 45 to match the maximum version level needed by the given file (e.g., 20 for Deflate, 45 for ZIP64).

  • In the local file header table, EPUB Creators MUST set the compression method field to the values 0 or 8.

OCF ZIP Container Media Type Identification

EPUB Creators MUST include the mimetype file as the first file in the OCF ZIP Container. In addition:

  • The contents of the mimetype file MUST be the MIME media type [[RFC2046]] string application/epub+zip encoded in US-ASCII [[US-ASCII]].
  • The mimetype file MUST NOT contain any leading or trailing padding or white space.
  • The mimetype file MUST NOT begin with the Unicode byte order mark U+FEFF.
  • EPUB Creators MUST NOT compress or encrypt the mimetype file, and MUST NOT include an extra field in its ZIP header.

Refer to for further information about the application/epub+zip media type.

Resource Obfuscation

Introduction

Since an OCF ZIP Container is fundamentally a ZIP file, commonly available ZIP tools can be used to extract any unencrypted content stream from the package. Moreover, the nature of ZIP files means that their contents might appear like any other native container on some systems (e.g., a folder).

While this simplicity of ZIP files is quite useful, it also poses a problem when ease of extraction of resources is not a desired side-effect of not encrypting them. An EPUB Creator who wishes to include a third-party font, for example, typically does not want that font extracted and re-used by others. More critically, many commercial fonts allow embedding, but embedding a font implies making it an integral part of the EPUB Publication, not just providing the original font file along with the content.

Since integrated ZIP support is so ubiquitous in modern operating systems, simply placing a font in the ZIP archive is insufficient to signify that the font cannot be reused in other contexts. This uncertainty can undermine the otherwise useful font embedding capability of EPUB Publications.

To discourage reuse of the font, some font vendors might only allow use of their fonts in EPUB Publications if those fonts are bound in some way to the EPUB Publication. That is, if the font file cannot be installed directly for use on an operating system with the built-in tools of that computing device, and it cannot be directly used by other EPUB Publications.

It is beyond the scope of this specification to provide a digital rights management or enforcement system for such resources. This section instead defines a method of obfuscation that will require additional work on the part of the final OCF recipient to gain general access to any obfuscated resources.

Note this specification does not claim that this constitutes encryption, nor does it guarantee that the resource will be secure from copyright infringement. The hope is that this algorithm will meet the requirements of most vendors who require some assurance that their resources cannot simply be extracted by unzipping the Container.

In the case of fonts, the primary use case for obfuscation, the defined mechanism will simply provide a stumbling block for those who are unaware of the license details. It will not prevent a determined user from gaining full access to the font. Given an OCF Container, it is possible to apply the algorithms defined to extract the raw font file. Whether this method of obfuscation satisfies the requirements of individual font licenses remains a question for the licensor and licensee.

Obfuscation Key

EPUB Creators MUST derive the key used in the obfuscation algorithm from the Unique Identifier.

All white space characters, as defined in section 2.3 of the XML 1.0 specification [[XML]], MUST be removed from this identifier — specifically, the Unicode code points U+0020, U+0009, U+000D and U+000A.

EPUB Creators SHOULD generate a SHA-1 digest of the UTF-8 representation of the resulting string as specified by the Secure Hash Standard [[FIPS-180-4]]. They can then use this digest as the key for the algorithm.

Obfuscation Algorithm

The algorithm employed to obfuscate resource consists of modifying the first 1040 bytes (~1KB) of the file. (In the unlikely event that the file is less than 1040 bytes, this process will modify the entire file.)

To obfuscate the original data, store, as the first byte of the embedded resource, the result of performing a logical exclusive or (XOR) on the first byte of the raw file and the first byte of the obfuscation key.

Repeat this process with the next byte of source and key and continue for all bytes in the key. At this point, the process continues starting with the first byte of the key and 21st byte of the source. Once 1040 bytes are encoded in this way (or the end of the source is reached), directly copy any remaining data in the source to the destination.

EPUB Creators MUST obfuscate resources before compressing and adding them to the OCF Container. Note that as obfuscation is not encryption, this requirement is not a violation of the one in to compress resources before encrypting them.

Specifying Obfuscated Resources

Although not technically encrypted data, all obfuscated resources MUST have an entry in the encryption.xml file accompanying the EPUB Publication (see ).

EPUB Creators MUST specify an EncryptedData element for each obfuscated resource. Each EncryptedData element MUST contain a child EncryptionMethod element whose Algorithm attribute has the value http://www.idpf.org/2008/embedding. The presence of this attribute signals the use of the algorithm described in this specification. EPUB Creators MUST list the path to the obfuscated resource in the CipherReference child of the CipherData element.

To prevent trivial copying of the embedded resource to other EPUB Publications, EPUB Creators MUST NOT provide the obfuscation key in the encryption.xml file.

Media Overlays

Introduction

Mainstream ebooks, educational tools and ebooks formatted for persons with print disabilities are some examples of works that contain synchronized audio narration. In EPUB 3, EPUB Creators can create these types of books using Media Overlay Documents to describe the timing for the pre-recorded audio narration and how it relates to the EPUB Content Document markup. The specification defines the file format for Media Overlays as a subset of [[SMIL3]], a W3C recommendation for representing synchronized multimedia information in XML.

The text and audio synchronization enabled by Media Overlays provides enhanced accessibility for any user who has difficulty following the text of a traditional book. Media Overlays also provide a continuous listening experience for readers who are unable to read the text for any reason, something that traditional audio embedding techniques cannot offer. They are even useful for purposes not traditionally considered accessibility concerns (e.g., for language learning).

The Media Overlays feature is transparent to EPUB Reading Systems that do not support the feature. The inclusion of Media Overlays in an EPUB Publication has no impact on the ability of Media Overlay-unaware Reading Systems to render the EPUB Publication as though the Media Overlays are not present.

Media Overlays in EPUB are not an equivalent to audiobooks, as audiobooks are primarily audio-based with text occasionally provided as an alternate format. The W3C [[Audiobooks]] recommendation is for building audio publications.

Although future versions of this specification might incorporate support for video media (e.g., synchronized text/sign-language books), this version supports only synchronizing audio media with the EPUB Content Document.

Media Overlay Documents

Media Overlay Document Requirements

A Media Overlay Document:

  • MUST be valid to the Media Overlays schema as defined in and conform to all content conformance constraints expressed in .

  • MAY refer to more than one EPUB Content Document, but more than one Media Overlay Document MUST NOT reference the same EPUB Content Document.

  • SHOULD use semantic markup where appropriate.

Media Overlay Document Definition

All elements [[XML]] defined in this section are in the https://www.w3.org/ns/SMIL namespace [[XML-NAMES]] unless otherwise specified.

The smil Element

The smil element is the root element of all Media Overlay Documents.

Element Name

smil

Usage

The smil element is the root element of the Media Overlay Document.

Attributes
version [required]

Specifies the version number of the [[SMIL3]] specification to which the Media Overlay adheres.

This attribute MUST have the value "3.0".

id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

epub:prefix [optional]

Declares additional metadata vocabulary prefixes.

Refer to for more information.

Content Model

In this order:

The head Element

The head element is the container for metadata in the Media Overlay Document.

Element Name

head

Usage

The head element is the OPTIONAL first child of the smil element.

Attributes

None

Content Model

metadata [0 or 1]

As this specification does not define any metadata properties that must occur in the Media Overlay Document, the head element is OPTIONAL.

The metadata Element

The metadata element represents metadata for the Media Overlay Document. The metadata element is an extension point that allows the inclusion of metadata from any metainformation structuring language.

Element Name

metadata

Usage

As a child of the head element.

Attributes

None

Content Model

[0 or more] elements from any namespace

This specification defines no metadata properties that MUST occur in the Media Overlay Document; the metadata element is provided for custom metadata requirements.

The body Element

The body element is the starting point for the presentation contained in the Media Overlay Document. It contains the main sequence of par and seq elements.

Element Name

body

Usage

The body element is the REQUIRED second child of the smil element.

Attributes
epub:type [optional]

An expression of the structural semantics of the corresponding element in the EPUB Content Document.

The value is a white space separated list of property types. Refer to for more information.

id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

epub:textref [optional]

Identifies an associated fragment of an EPUB Content Document.

The value MUST be a relative-URL-with-fragment string [[URL]] with a fragment identifier.

Content Model

In any order:

MUST include at least one par or seq.

The seq Element

The seq element contains a sequential rendering of media objects.

Element Name

seq

Usage

One or more seq elements MAY occur as children of the body element and of the seq element.

Attributes
epub:type [optional]

An expression of the structural semantics of the corresponding element in the EPUB Content Document.

The value is a white space separated list of property types. Refer to for more information.

id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

epub:textref [required]

Identifies an associated fragment of an EPUB Content Document.

The value MUST be a relative-URL-with-fragment string [[URL]] with a fragment identifier.

Refer to for more information.

Content Model

In any order:

MUST include at least one par or seq.

The par Element

The par element defines the parallel rendering of media objects.

Element Name

par

Usage

One or more par elements MAY occur as children of the body and seq elements.

Attributes
epub:type [optional]

An expression of the structural semantics of the corresponding element in the EPUB Content Document.

The value is a white space separated list of property types. Refer to for more information.

id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

Content Model

In any order:

The audio element is OPTIONAL only if its sibling text element refers to audio or video media (see ), or to textual content intended for rendering via Text-to-Speech (TTS).

The text Element

The text element references an element in the EPUB Content Document. A text element typically refers to a textual element but can also refer to other EPUB Content Document media elements (see ).

Element Name

text

Usage

As a REQUIRED child of the par element.

Attributes
src [required]

Identifies the associated fragment of an EPUB Content Document.

The value MUST be a relative-URL-with-fragment string [[URL]] with a fragment identifier.

id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

Content Model

Empty

The audio Element

The audio element represents a clip of audio media.

Element Name

audio

Usage

A REQUIRED child of the par element unless its sibling text element refers to audio or video media, or to textual content intended for rendering via Text-to-Speech (TTS), in which case it is OPTIONAL (see ).

Attributes
id [optional]

The ID [[XML]] of the element, which MUST be unique within the document scope.

src [required]

The relative- or absolute-URL string [[URL]] reference to an audio file. The audio file MUST be one of the audio formats listed in the Core Media Type Resources table.

clipBegin [optional]

A clock value that specifies the offset into the physical media corresponding to the start point of an audio clip.

MUST be a [[SMIL3]] clock value.

See .

clipEnd [optional]

A clock value that specifies the offset into the physical media corresponding to the end point of an audio clip.

MUST be a [[SMIL3]] clock value.

See .

The chronological offset of the terminating position MUST be after the starting offset specified in the clipBegin attribute.

Content Model

Empty

Creating Media Overlays

Introduction

EPUB Creators can represent a pre-recorded narration of a publication as a series of audio clips, each corresponding to part of an EPUB Content Document. A single audio clip, for example, typically represents a single phrase or paragraph, but infers no order relative to the other clips or to the text of a document. Media Overlays solve this problem of synchronization by tying the structured audio narration to its corresponding text (or other media) in the EPUB Content Document using [[SMIL3]] markup. Media Overlays are, in fact, a simplified subset of SMIL 3.0 that define the playback sequence of these clips.

The SMIL elements primarily used for structuring Media Overlays are body (used for the main sequence), seq (sequence) and par (parallel). (Refer to for more information on these and other SMIL elements.)

The par element is the basic building block of an Overlay and corresponds to a phrase in the EPUB Content Document. The element provides two key pieces of information for synchronizing content: 1) the audio clip containing the narration for the phrase; and 2) a pointer to the associated EPUB Content Document fragment. The par element uses two media element children to represent this information: an audio element and a text element. Since par elements render their children in parallel, Reading Systems play the audio clip and EPUB Content Document fragment at the same time, resulting in a synchronized presentation.

The text element src attribute references the associated phrase, sentence, or other segment of the EPUB Content Document by its URL [[URL]] reference. The audio element src attribute similarly references the location of the corresponding audio clip and adds the OPTIONAL clipBegin and clipEnd attributes to indicate a specific offset within the clip.

EPUB Creators place par elements together sequentially to form a series of phrases or sentences. Not every element of the EPUB Content Document will have a corresponding par element in the Media Overlay, only those relevant to the audio narration.

EPUB Creators can also add par elements to seq elements to define more complex structures such as parts and chapters (see ).

Relationship to the EPUB Content Document

In this section, the EPUB Content Document is assumed to be an XHTML Content Document. While EPUB Creators may use Media Overlays with SVG Content Documents, playback behavior might not be consistent and therefore interoperability is not guaranteed.

Overlay Structure

The body of a Media Overlay Document consists of two elements: the par element and the seq element. The ordering of these elements represents how Reading Systems render the content in the corresponding EPUB Content Documents during playback.

The par element represents phrases. Each element identifies a text and audio component to synchronize during playback.

The seq element represents sequences. EPUB Creators can use it to represent nested containers such as sections, asides, headers, and footnotes. It allows EPUB Creators to retain the structure inherent in these containers in the Media Overlay Document.

The seq element MUST contain an epub:textref attribute. As seq elements do not provide synchronization instructions, this attribute allows a Reading System to match the fragment to a location in the text.

The following example shows a Media Overlay Document with nested seq elements, representing a chapter with both a section header and a figure.

<smil xmlns="http://www.w3.org/ns/SMIL" xmlns:epub="http://www.idpf.org/2007/ops" version="3.0">
    <body>

        <!-- a chapter -->
        <seq id="id1" epub:textref="chapter1.xhtml#sectionstart" epub:type="chapter">

            <!-- the section title -->
            <par id="id2">
                <text src="chapter1.xhtml#section1_title"/>
                <audio src="chapter1_audio.mp3"
                       clipBegin="0:23:23.84"
                       clipEnd="0:23:34.221"/>
            </par>

            <!-- some sentences in the chapter -->
            <par id="id3">
                <text src="chapter1.xhtml#text1"/>
                <audio src="chapter1_audio.mp3"
                       clipBegin="0:23:34.221"
                       clipEnd="0:23:59.003"/>
            </par>
            <par id="id4">
                <text src="chapter1.xhtml#text2"/>
                <audio src="chapter1_audio.mp3"
                       clipBegin="0:23:59.003"
                       clipEnd="0:24:15.000"/>
            </par>

            <!-- a figure -->
            <seq id="id7" epub:textref="chapter1.xhtml#figure">
                <par id="id8">
                    <text src="chapter1.xhtml#photo"/>
                    <audio src="chapter1_audio.mp3"
                           clipBegin="0:24:18.123"
                           clipEnd="0:24:28.764"/>
                </par>
                <par id="id9">
                    <text src="chapter1.xhtml#caption"/>
                    <audio src="chapter1_audio.mp3"
                           clipBegin="0:24:28.764"
                           clipEnd="0:24:50.010"/>
                </par>
            </seq>

            <!-- more sentences in the chapter (outside the figure) -->
            <par id="id12">
                <text src="chapter1.xhtml#text3"/>
                <audio src="chapter1_audio.mp3"
                       clipBegin="0:25:45.515"
                       clipEnd="0:26:30.203"/>
            </par>
            <par id="id13">
                <text src="chapter1.xhtml#text4"/>
                <audio src="chapter1_audio.mp3"
                       clipBegin="0:26:30.203"
                       clipEnd="0:27:15.000"/>
            </par>

        </seq>
    </body>
</smil>

The reason for grouping structures like sections, figures, tables, and footnotes in a seq element is so that Reading Systems can identify their start and end positions during playback. Reading Systems can then offer playback options tailored to the layout of the content, such as jumping past a long figure, turning off rendering of page break announcements (see ), or customizing the reading mode to suit structures such as tables.

Referencing Document Fragments

The epub:textref attribute and the text element's src attribute both require a fragment identifier that references a specific fragment (e.g., an element or text string) of the associated EPUB Content Document.

For XHTML and SVG Content Documents, the fragment SHOULD be a reference to a target element [[HTML]] or an SVG Fragment Identifier [[SVG]], respectively.

EPUB Creators MAY use other fragment identifier schemes, but Reading Systems may not support such identifiers.

Overlay Granularity

The granularity level of the Media Overlay depends on how EPUB Creators mark up the EPUB Content Document and the type of fragment identifier they use in the text elements' src attributes. For example, when referencing target elements [[HTML]], if the finest level of markup is at the paragraph level, then that is the finest possible level for Media Overlay synchronization. Likewise, if sub-paragraph markup is available, such as [[HTML]] span elements representing phrases or sentences, then finer granularity is possible in the Media Overlay. Finer granularity gives users more precise results for synchronized playback when navigating by word or phrase and when searching the text but increases the file size of the Media Overlay Documents. Fragment identifier schemes that do not rely on the presence of elements could provide even finer granularity, where supported.

Embedded Media

Any EPUB Content Document associated with a Media Overlay MAY contain embedded media such as video, audio, and images. EPUB Creators MAY use the Media Overlay text element in such instances to reference the embedded media by its element's id attribute value.

When a text element references embedded media that contains audio, the audio sibling element is OPTIONAL.

EPUB Creators SHOULD avoid using scripts to control playback of referenced embedded EPUB Content Document media, as this might conflict with Media Overlays playback behavior.

EPUB Creators should carefully examine any overlapping audio situations and deal with them at the production stage, as Reading Systems handling of simultaneous volume levels is optional.

Text-to-Speech Rendering

This specification allows the use of Text-to-Speech (TTS) in addition to pre-recorded audio clips. When a Media Overlay text element with no sibling audio element references an element within the target EPUB Content Document, the contents of the referenced fragment MUST be appropriate for rendering via TTS. For example, it could be a textual EPUB Content Document element or contain a text fallback.

Structural Semantics in Overlays

To express structural semantics in Media Overlay Documents, EPUB Creators MAY specify the epub:type attribute on par, seq, and body elements.

The epub:type attribute facilitates Reading System behavior appropriate for the semantic type(s) indicated. Examples of these behaviors are skippability and escapability and table reading mode [[?EPUB-RS-33]].

Media Overlays MAY use the applicable vocabulary association mechanisms for the epub:type attribute to define additional semantics.

Associating Style Information

EPUB Creators MAY express visual rendering information for the currently playing EPUB Content Document element in a CSS Style Sheet using author-defined classes.

When used, EPUB Creators MUST declare the class names in the Package Document using the active-class and playback-active-class properties.

EPUB Creators MUST define exactly one CSS class name in each property they define. Each property MUST define a valid CSS class name not including any selectors [[CSS2]]. This specification does not reserve names for use with these properties.

EPUB Creators MAY define any CSS properties for the specified CSS classes, but must ensure that each EPUB Content Document with an associated Media Overlay Document includes a link to the CSS style sheet with the class definitions. Reading Systems might provide their own styling, or no styling at all, in the absence of a linked definition.

EPUB Creators MUST NOT use the active-class and playback-active-class properties in conjunction with a refines attribute as they always apply to the entire EPUB Publication.

Media Overlays Packaging

Including Media Overlays

If an EPUB Content Document is wholly or partially referenced by a Media Overlay, then its manifest item element MUST specify a media-overlay attribute. The attribute MUST reference the ID [[XML]] of the manifest item for the corresponding Media Overlay Document.

EPUB Creators MUST only specify the media-overlay attribute on manifest item elements that reference EPUB Content Documents.

Manifest items for Media Overlay Documents MUST have the media type application/smil+xml.

Overlays Package Metadata

EPUB Creators MUST specify the duration of the entire EPUB Publication in the Package Document using a meta element with the duration property.

In addition, EPUB Creators MUST provide the duration of each Media Overlay Document. EPUB Creators may use the refines attribute to associate each duration declaration to the corresponding manifest item.

The sum of the durations for each Media Overlay Document SHOULD equal the total duration.

EPUB Creators MAY also specify narrator information in the Package Document, as well as author-defined CSS class names to apply to the currently playing EPUB Content Document element.

The media: prefix is reserved for inclusion of these properties in package metadata.

Skippability and Escapability

Skippability

While reading, users may want to turn on or off certain features of the content, such as footnotes, page numbers, or other types of secondary content. This feature is called skippability. Reading Systems use the semantic information provided by Media Overlay elements' epub:type attribute to determine when to offer users the option of skippable features.

The following non-exhaustive list represents terms from the Structural Semantics Vocabulary for which Reading Systems may offer the option of skippability:

  • footnote

  • endnote

  • pagebreak

Reading System are not required to support for skippability based on epub:type values.

Escapability

Escapable items are nested structures, such as tables and lists, that users might wish to skip over, continuing to read from the point immediately after the nested structure. The escapability feature differs from the skippability feature in that it does not enable or disable entire types of items, but provides an exit from them (e.g., a user can listen to some of the content before choosing to escape).

The following non-exhaustive list represents terms from the Structural Semantics Vocabulary for which Reading Systems may offer the option of escapability:

  • table

  • table-row

  • table-cell

  • list

  • list-item

  • figure

Navigation Document Overlays

As the EPUB Navigation Document is an XHTML Content Document, EPUB Creators MAY associate an audio Media Overlay with it. Unlike traditional XHTML Content Documents, however, Reading Systems must present the EPUB Navigation Document to users even when it is not included in the spine (see Navigation Document Processing [[?EPUB-RS-33]]). As a result, the method in which an associated Media Overlay behaves can change depending on the context:

Specific implementation details are beyond the scope of this specification. The DAISY Media Overlays Playback Requirements document describes best practices for EPUB Creators and provides recommendations for Reading System developers.

Accessibility

EPUB 3 builds upon the Open Web Platform expressly so that it can leverage the structure, semantics and, by extension, accessibility built into its underlying technologies.

The requirements and practices for creating accessible web content have already been documented in the W3C's Web Content Accessibility Guidelines (WCAG) [[WCAG2]]. These guidelines also form the basis for defining accessibility in EPUB Publications.

As the current WCAG guidelines (version 2) are heavily focused on web pages, a separate specification, EPUB Accessibility [[EPUB-A11Y-11]], defines how to apply the standard to EPUB Publications. It also adds EPUB-specific requirements and recommendations for metadata, pagination, and media overlays.

This specification recommends that EPUB Publications conform to the EPUB Accessibility standard. A benefit of following this recommendation is that it helps ensure that EPUB Publications meet the accessibility requirements legislated in jurisdictions around the world, ensuring EPUB Creators are not locked out of potential markets.

EPUB Creators, however, should look beyond legal imperatives and treat accessibility as a requirement for all their content. The more accessible that EPUB Publications are, the greater the potential audience for them.

This specification does not integrate the accessibility requirements to allow them to adapt and evolve independent of the EPUB specification — accessibility practices often need more frequent updating. The accessibility specification is also intended for use with past, present, and future versions of EPUB. The approach of a separate specification ensures that the evolution of EPUB does not lock accessibility in time (i.e., it allows producers of older versions of EPUB to reference the latest accessibility requirements).

Security and Privacy

This is a very initial draft intended only as a starting point. It is inspired by the relevant section of the Publication Manifest specification. It will require more work.

The particularity of an EPUB Publication is its structure. 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. This specification does not add any new features, APIs, etc. This also means that, essentially, the security and privacy issues are reliant on the features of those formats. In particular:

The Working Group will have to address the particularity of cross-origin by addressing the question of what the "origin" is for an EPUB Publication.

Unsupported Features

This specification contains certain features the Working Group no longer recommends for use or that are only retained for legacy support reasons. This section defines the meanings of the designations attached to these features and their support expectations.

Deprecated Features

A deprecated feature is one the Working Group no longer recommends for use in this version of the specification. Deprecated features typically have limited or no support in Reading Systems and/or usage in EPUB Publications. If this specification designates a feature as deprecated, the following hold true:

Validation tools SHOULD alert EPUB Creators to the presence of deprecated features when encountered in EPUB Publications.

Legacy Features

A legacy feature is one that the Working Group has retained only for authoring content that is compatible with versions of EPUB prior to 3.0. If this specification designates a feature as legacy, the following hold true:

Validation tools SHOULD NOT alert EPUB Creators about the presence of legacy features in an EPUB Publication, as their inclusion is valid for backwards compatibility. Validation tools MUST alert EPUB Creators if a legacy feature does not conform to its definition or otherwise breaks a usage requirement.

Allowed External Identifiers

The following table lists the public and system identifiers [[XML]] allowed in document type declarations. [[XML]]

EPUB Creators MAY use these external identifiers only in Publication Resources with the listed media types specified in their manifest declarations. (Refer to for more information.)

Media Type(s) Public Identifier System Identifier
  • application/mathml+xml
  • application/mathml-presentation+xml
  • application/mathml-content+xml
-//W3C//DTD MathML 3.0//EN http://www.w3.org/Math/DTD/mathml3/mathml3.dtd
application/svg+xml -//W3C//DTD SVG 1.1//EN http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd

Expressing Structural Semantics

Introduction

Structural semantics add additional meaning about the specific structural purpose an element plays. The epub:type attribute is used to express domain-specific semantics in EPUB Content Documents and Media Overlay Documents, with the structural information it carries complementing the underlying vocabulary.

The applied semantics refine the meaning of their containing elements; they do not override their nature (e.g., EPUB Creators can use the attribute to indicate a [[HTML]] section is a chapter in a work, but not to turn p elements into list items to avoid proper list structures).

Semantic metadata enriches content for use in publishing workflows and for author-defined purposes. It also allows Reading Systems to learn more about the structure and content of a document (e.g., to enable skippability and escapability in Media Overlays).

This specification defines a method for adding structural semantics using the attribute axis: instead of adding new elements, EPUB Creators can append the epub:type attribute to existing elements to add the desired semantics.

The epub:type Attribute

Attribute Name

type

Namespace

http://www.idpf.org/2007/ops

Usage

Global attribute. EPUB Creators MAY specify on all elements.

Value

A white space-separated list of property values, with restrictions as defined in .

White space is the set of characters as defined in [[XML]].

The epub:type attribute inflects semantics on the element on which it appears. Its value is one or more white space-separated terms stemming from external vocabularies associated with the document instance.

The inflected semantic MUST express a subclass of the semantic of the carrying element. In the case of semantically neutral elements, such as the [[HTML]] div and span elements, the inflected semantic MUST NOT attach a meaning that is already conveyed by an existing element (e.g., that a div represents a paragraph or section).

Although the epub:type attribute is similar in nature to the role attribute [[HTML]], the attributes serve different purposes. The values of the epub:type attribute do not enhance the accessibility of EPUB Publications, for example, they do not map to accessibility APIs used by assistive technologies. The epub:type attribute is only intended for publishing semantics and Reading System enhancements. Refer to Digital Publishing WAI-ARIA Module 1.0 [[DPUB-ARIA-1.0]] for more information about accessible publishing roles.

The default vocabulary for the epub:type attribute is the Structural Semantics Vocabulary. EPUB Creators MAY include unprefixed terms that are not part of this vocabulary, but the preferred method for adding custom semantics is to use prefixes for them. Refer to for more information.

Vocabularies

This appendix defines a general set of mechanisms by which attributes in this specification can reference terms from vocabularies. It also defines EPUB-specific vocabularies for use with the attributes.

Vocabulary Association Mechanisms

Introduction

EPUB defines a formal method of referencing terms and properties defined in metadata and semantic vocabularies using the property data type. The epub:type attribute uses this data type in EPUB Content Documents and Media Overlay Documents to add structural semantics, for example, while the property and rel attributes use the data type to define properties and relationships in the Package Document.

A property value is like a CURIE [[RDFA-CORE]] — it represents a URL [[URL]] in compact form. The expression consists of a prefix and a reference, where the prefix — whether literal or implied — is a shorthand mapping of a URL that typically resolves to a term vocabulary. When a Reading System converts the prefix to its URL representation and combines with the reference, the resulting URL normally resolves to a fragment within that vocabulary that contains human- and/or machine-readable information about the term.

To reduce the complexity for authoring, each attribute that takes a property data type also defines a default vocabulary. Terms and properties referenced from the default vocabularies do not include a prefix as the mapping Reading Systems use to map to a URL is predefined.

The power of the property data type lies in its easy extensibility. To incorporate new terms and properties, EPUB Creators only need to declare a prefix. In another authoring convenience, this specification also reserves prefixes for many commonly used publishing vocabularies (i.e., their declaration is optional).

The following sections provide additional details on the property data type and vocabulary association mechanism.

The property Data Type

The property data type is a compact means of expressing a URL [[URL]] and consists of an OPTIONAL prefix separated from a reference by a colon.

(EBNF productions ISO/IEC 14977)
All terminal symbols are in the Unicode Block 'Basic Latin' (U+0000 to U+007F).
property = [ prefix , ":" ] , reference;  
prefix = ? xsd:NCName ? ;  
reference = ? path-relative-scheme-less-URL string [[URL]] ? ; /* as defined in [[URL]] */

This specification derives the property data type from the CURIE data type defined in [[RDFA-CORE]]. A property represents a subset of CURIEs.

After processing [[EPUB-RS-33]], this property would expand to the following URL:

http://purl.org/dc/terms/modified

as the dcterms: prefix is a reserved prefix that maps to the URL "http://purl.org/dc/terms/".

When an EPUB Creator omits a prefix from a property value, the expressed reference represents a term from the default vocabulary for that attribute.

An empty string does not represent a valid property value, even though it is valid to the definition above.

Default Vocabularies

A default vocabulary is one that EPUB Creators do not have to declare a prefix for in order to use its terms and properties where a property value is expected. EPUB Creators MUST NOT add a prefix to terms and properties from a default vocabulary.

EPUB Creators MUST NOT assign a prefix to the URLs associated with these vocabularies using the prefix attribute.

Refer to the definition of each attribute that takes a property data type for more information about its default vocabulary.

The prefix Attribute

The prefix attribute defines prefix mappings for use in property values.

The value of the prefix attribute is a white space-separated list of one or more prefix-to-URL mappings of the form:

(EBNF productions ISO/IEC 14977)
All terminal symbols are in the Unicode Block 'Basic Latin' (U+0000 to U+007F).
prefixes = mapping , { whitespace, { whitespace } , mapping } ;  
mapping = prefix , ":" , space , { space } , ? xsd:anyURI ? ;  
prefix = ? xsd:NCName ? ;  
space = #x20 ;  
whitespace = (#x20 | #x9 | #xD | #xA) ;  

EPUB Creators MUST only specify the prefix attribute on the root element of the respective format.

The attribute is not namespaced when used in the Package Document.

EPUB Creators MUST declare the attribute in the namespace http://www.idpf.org/2007/ops in EPUB Content Documents and Media Overlay Documents.

Although the prefix attribute is modeled on the identically named prefix attribute in [[RDFA-CORE]], EPUB Creators cannot use the attributes interchangeably. The prefix attribute without a namespace in EPUB Content Documents is the RDFa attribute.

It is common for both attributes to appear in EPUB Content Documents that also specify RDFa expressions.

<html … prefix="…"
        xmlns:epub="http://www.idpf.org/2007/ops"
        epub:prefix="…">   …
</html>

Note that for embedded SVG, prefixes MUST be declared on the [[HTML]] root html element.

To avoid conflicts, EPUB Creators MUST NOT use the prefix attribute to declare a prefix that maps to the default vocabulary.

EPUB Creators MUST NOT declare the prefix '_' as this specification reserves this prefix for future compatibility with RDFa [[RDFA-CORE]] processing.

For future compatibility with alternative serializations of the Package Document, EPUB Creators MUST NOT declare a prefix for the Dublin Core /elements/1.1/ namespace [[DCTERMS]]. EPUB Creators MUST use only the [[DCTERMS]] elements allowed in the Package Document metadata.

Reserved Prefixes

Although reserved prefixes are an authoring convenience, EPUB Creators should avoid relying on them as they may cause interoperability issues. Validation tools will often reject new prefixes until their developers update the tools to the latest version of the specification, for example. EPUB Creators should declare all prefixes they use to avoid such issues.

EPUB Creators MAY use reserved prefixes in attributes that expect a property value without declaring them in a prefix attribute.

EPUB Creators SHOULD NOT override reserved prefixes in the prefix attribute.

The reserved prefixes an EPUB Creators can use depends on the context:

Package Document

EPUB Creators MAY use the following prefixes in Package Document attributes without having to declare them.

Prefix URL
a11y http://www.idpf.org/epub/vocab/package/a11y/#
dcterms http://purl.org/dc/terms/
marc http://id.loc.gov/vocabulary/
media http://www.idpf.org/epub/vocab/overlays/#
onix http://www.editeur.org/ONIX/book/codelists/current.html#
rendition http://www.idpf.org/vocab/rendition/#
schema http://schema.org/
xsd http://www.w3.org/2001/XMLSchema#
Structural Semantics

EPUB Creators MAY use the following reserved prefixes in the epub:type attribute without having to declare them.

Prefix URL
msv http://www.idpf.org/epub/vocab/structure/magazine/#
prism http://www.prismstandard.org/specifications/3.0/PRISM_CV_Spec_3.0.htm#

Prefixed CSS Properties

This appendix describes the prefixed CSS properties supported by EPUB.

CSS Writing Modes

This section describes the -epub- prefixed properties for [[CSS-Writing-Modes-3]].

The -epub-text-orientation Property

This is a prefixed version of the CSS text-orientation property.

Name: -epub-text-orientation
Value: mixed | upright | sideways | sideways-right

Previous versions of EPUB 3 used additional values of -epub-text-orientation. User agents MUST interpret these values according to the following table:

Deprecated value Value to be used
vertical-right mixed
rotate-right sideways
rotate-normal sideways
The -epub-writing-mode Property

This is a prefixed version of the CSS writing-mode property, with the same syntax and behavior.

Name: -epub-writing-mode
Value: horizontal-tb | vertical-rl | vertical-lr
The -epub-text-combine-horizontal and -epub-text-combine Properties

These are prefixed versions of text-combine-upright, although -epub-text-combine is deprecated. See the table below for how values of both properties translate to unprefixed CSS.

Name: -epub-text-combine-horizontal
Value: none | all
Name: -epub-text-combine (deprecated)
Value: none | horizontal | horizontal <number>

The following table shows how to map from the prefixed versions to the current CSS versions.

Prefixed version CSS equivalent
-epub-text-combine-horizontal: none text-combine-upright: none
-epub-text-combine-horizontal: all text-combine-upright: all
-epub-text-combine: none text-combine-upright: none
-epub-text-combine: horizontal text-combine-upright: all
-epub-text-combine: horizontal <number> Error
CSS Text Level 3

This section describes the -epub- prefixed properties (and one prefixed value) for [[CSS-Text-3]].

The -epub-hyphens Property

This is a prefixed version of the hyphens property.

Name: -epub-hyphens
Value: none | manual | auto | all

The all value is no longer supported in CSS.

The -epub-line-break Property

This is a prefixed version of the line-break property.

Name: -epub-line-break
Value: auto | loose | normal | strict
The -epub-text-align-last Property

This is a prefixed version of the text-align-last property.

Name: -epub-text-align-last
Value: auto | start | end | left | right | center | justify
The -epub-word-break Property

This is a prefixed version of the word-break property.

Name: -epub-word-break
Value: normal | keep-all | break-all
The text-transform Property

This is a prefixed value for the text-transform property.

Name: text-transform
Value: -epub-fullwidth

The following table describes the equivalent value in CSS.

EPUB version CSS equivalent
text-transform: -epub-fullwidth text-transform: full-width
CSS Text Decoration Level 3

This section describes the -epub- prefixed properties for [[CSS-Text-Decor-3]].

The -epub-text-emphasis-color Property

This is a prefixed version of the text-emphasis-color property.

Name: -epub-text-emphasis-color
Value: <color>
The -epub-text-emphasis-position Property

This is a prefixed version of the text-emphasis-position property.

Name: -epub-text-emphasis-position
Value: [ over | under ] && [ right | left ]
The -epub-text-emphasis-style Property

This is a prefixed version of the text-emphasis-style property.

Name: -epub-text-emphasis-style
Value: none | [ [ filled | open ] || [ dot | circle | double-circle | triangle | sesame ] ] | <string>
The -epub-text-underline-position Property

This is a prefixed version of the text-underline-position property. One value is no longer supported by CSS.

Name: -epub-text-underline-position
Value: auto | [ under || [ left | right ] ] | alphabetic

The following table describes the equivalent value in CSS.

EPUB version CSS equivalent
-epub-text-underline-position: alphabetic text-underline-position: auto

Schemas

Package Document Schema

A non-normative schema for Package Documents is available at https://github.com/w3c/epubcheck/tree/master/src/main/resources/com/adobe/epubcheck/schema/30/package-30.nvdl.

Validation using this schema requires a processor that supports [[NVDL]], [[RelaxNG-Schema]], [[ISOSchematron]] and [[XMLSCHEMA-2]].

The NVDL schema layer can be substituted by a multi-pass validation using the embedded RELAX NG and ISO Schematron schemas alone.

These schemas may be updated and corrected outside of formal revisions of this specification. As a result, they are subject to change at any time.

OCF Schemas

Schema for container.xml

A non-normative schema for container.xml files is available at https://github.com/w3c/epubcheck/tree/master/src/main/resources/com/adobe/epubcheck/schema/30/ocf-container-30.nvdl.

Validation using this schema requires a processor that supports [[RelaxNG-Schema]] and [[XMLSCHEMA-2]].

Schema for encryption.xml

The schema for encryption.xml files is included in [[XMLSEC-RNGSCHEMA-20130411]].

Schema for signatures.xml

The schema for signatures.xml files is included in [[XMLSEC-RNGSCHEMA-20130411]].

Media Overlays Schema

A non-normative schema for Media Overlays is available at https://github.com/w3c/epubcheck/tree/main/src/master/resources/com/adobe/epubcheck/schema/30/media-overlay-30.nvdl.

Validation using this schema requires a processor that supports [[NVDL]], [[RelaxNG-Schema]], [[ISOSchematron]] and [[XMLSCHEMA-2]].

The NVDL schema layer can be substituted by a multi-pass validation using the embedded RELAX NG and ISO Schematron schemas alone.

Detailed Examples

Scripting Contexts

Consider the following example Package Document:

<package …>
    …
    <manifest>
        …
        <item id="chap01" 
            href="scripted01.xhtml" 
            media-type="application/xhtml+xml"
            properties="scripted"/>
        <item id="inset01" 
            href="scripted02.xhtml" 
            media-type="application/xhtml+xml"
            properties="scripted"/>
        <item id="slideshowjs" 
            href="slideshow.js" 
            media-type="text/javascript"/>
    </manifest>
    
    <spine …>
        <itemref idref="chap01"/>
        …
    </spine>
    …
</package>

and the following file scripted01.xhtml:

<html …>
    <head>
        …
        <script type="text/javascript">
            alert("Reading System name: " + navigator.epubReadingSystem.name);
        </script>
    </head>
    <body>
        …
        <iframe src="scripted02.xhtml" … />
        …
    </body>
</html>

and the following file scripted02.xhtml:

<html …>
    <head>
        …
        <script type="text/javascript" href="slideshow.js"></script>
    </head>
    <body>
        …
    </body>
</html>

From these examples, it is true that:

Packaged EPUB

The following example demonstrates the use of the OCF format to contain a signed and encrypted EPUB Publication within an OCF ZIP Container.

Clock Values

The following are examples of allowed clock values:

Media Type Registrations

The application/oebps-package+xml Media Type

This appendix registers the media type application/oebps-package+xml for the EPUB Package Document. This registration supersedes [[RFC4839]].

The Package Document is an XML file that describes an EPUB Publication. It identifies the resources in the EPUB Publication and provides metadata information. The Package Document and its related specifications are maintained and defined by the World Wide Web Consortium (W3C).

MIME media type name:

application

MIME subtype name:

oebps-package+xml

Required parameters:

None.

Optional parameters:

None.

Encoding considerations:

Package Documents are UTF-8 or UTF-16 encoded XML.

Security considerations:

Package Documents contain well-formed XML conforming to the XML 1.0 specification.

Clearly, it is possible to author malicious files which, for example, contain malformed data. Most XML parsers protect themselves from such attacks by rigorously enforcing conformance.

All processors that read Package Documents should rigorously check the size and validity of data retrieved.

There is no current provision in the EPUB 3 specification for encryption, signing, or authentication within the Package Document format.

Interoperability considerations:

None.

Published specification:

This media type registration is for the EPUB Package Document, as described by the EPUB 3 specification located at https://www.w3.org/TR/epub-33/.

The EPUB 3 specification supersedes the Open Packaging Format 2.0.1 specification, which is located at http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm and which also uses the application/oepbs-package+xml media type.

Applications which use this media type:

This media type is in wide use for the distribution of ebooks in the EPUB format.

Additional information:
Magic number(s):

none

File extension(s):

.opf

Macintosh File Type Code(s):

TEXT

Fragment Identifiers:

EPUB Canonical Fragment Identifiers are custom fragment identifiers that can resolve to application/oebps-package+xml documents.

Person & email address to contact for further information:

public-epub3@w3.org

Intended usage:

COMMON

Author/Change controller:

World Wide Web Consortium (W3C)

The application/epub+zip Media Type

This appendix registers the media type application/epub+zip for the EPUB Open Container Format (OCF).

An OCF ZIP Container, or EPUB Container, file is a container technology based on the [[ZIP]] archive format. It is used to encapsulate the EPUB Publication. OCF and its related standards are maintained and defined by the World Wide Web Consortium (W3C).

MIME media type name:

application

MIME subtype name:

epub+zip

Required parameters:

None.

Optional parameters:

None.

Encoding considerations:

OCF ZIP Container files are binary files encoded in the application/zip media type.

Security considerations:

All processors that read OCF ZIP Container files should rigorously check the size and validity of data retrieved.

In addition, because of the various content types that can be embedded in OCF ZIP Container files, application/epub+zip may describe content that poses security implications beyond those noted here. However, only in cases where the processor recognizes and processes the additional content, or where further processing of that content is dispatched to other processors, would security issues potentially arise. In such cases, matters of security would fall outside the domain of this registration document.

Security considerations that apply to application/zip also apply to OCF ZIP Container files.

Interoperability considerations:

None.

Published specification:

This media type registration is for the EPUB Open Container Format (OCF), as described by the EPUB 3 specification located at https://www.w3.org/TR/epub-33/.

The EPUB 3 specification supersedes both RFC 4839 and the Open Container Format 2.0.1 specification, which is located at http://www.idpf.org/doc_library/epub/OCF_2.0.1_draft.doc, and which also uses the application/epub+zip media type.

Applications that use this media type:

This media type is in wide use for the distribution of ebooks in the EPUB format.

Additional information:
Magic number(s):

0: PK 0x03 0x04, 30: mimetype, 38: application/epub+zip

File extension(s):

OCF ZIP Container files are most often identified with the extension .epub.

Macintosh file type code(s):

ZIP

Fragment identifiers:

EPUB Canonical Fragment Identifiers are custom fragment identifiers that can resolve to application/epub+zip and application/oebps-package+xml documents.

Person & email address to contact for further information:

public-epub3@w3.org

Intended usage:

COMMON

Author/change controller:

World Wide Web Consortium (W3C)

Change Log

Note that this change log only identifies substantive changes — those that affect the conformance of EPUB Publications or are similarly noteworthy.

For a list of all issues addressed during the revision, refer to the Working Group's issue tracker.

Substantive Changes since the Previous Working Draft

Substantive changes since EPUB 3.2