This specification defines semantics and conformance requirements for an EPUB® Package. Each Package represents one Rendition of an EPUB Publication, and is defined by a Package Document that describes the content of the Rendition and sets the requirements for how Publication Resources are associated.

This specification also defines the EPUB Navigation Document, a machine- and human-readable specialization of an EPUB Content Document that provides navigation aids such as the table of contents.

This specification is one of a family of specifications that compose [[EPUB32]], an interchange and delivery format for digital publications based on XML and Web Standards. It is meant to be read and understood in concert with the other specifications that make up EPUB 3

.

Refer to [[EPUB32Changes]] for more information on the differences between this specification and its predecessor.

Introduction

Terminology

Terms with meanings specific to EPUB 3 are capitalized in this document (e.g., "Author", "Reading System"). A complete list of these terms and definitions is provided in [[!EPUB32]].

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

Prefix Mappings

For convenience, the following reserved prefix mappings are used in this specification.

prefix URI
dcterms http://purl.org/dc/terms/
opf http://www.idpf.org/2007/opf
rendition http://www.idpf.org/vocab/rendition/#

Conformance

Package Conformance

A conformant EPUB Package MUST meet all of the following criteria:

Package Document

It MUST contain exactly one Package Document, which MUST conform to the content requirements defined in Package Document — Content Conformance.

Publication Resources

All Publication Resources associated with the Package MUST be listed in the Package Document (as defined in manifest).

EPUB Navigation Document

It MUST contain exactly one EPUB Navigation Document, which MUST conform to the content requirements defined in EPUB Navigation Documents — Content Conformance.

Content Documents

It MUST contain one or more EPUB Content Documents, each of which MUST conform to the content requirements defined in [[!ContentDocs32]].

CSS Style Sheets

It MAY contain zero or more CSS Style Sheets, each of which MUST conform to the content requirements defined in CSS Style Sheets — Content Conformance [[!ContentDocs32]].

Pronunciation Lexicons

It MAY contain zero or more PLS Documents, each of which MUST conform to the content requirements defined in PLS Documents — Content Conformance [[!ContentDocs32]].

Media Overlay Documents

It MAY contain zero or more Media Overlay Documents, each of which MUST conform to the content requirements defined in [[!MediaOverlays32]].

Additional Resources

It MAY contain zero or more Publication Resources in addition to those listed above, each of which MUST adhere to the requirements in Publication Resources [[!EPUB32]].

Reading System Conformance

An EPUB Reading System MUST meet all of the following criteria:

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 the EPUB Package. These elements serve to centralize metadata, detail the individual resources that compose the Package and provide the reading order and other information necessary to render the Rendition.

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

Content Conformance

A Package Document MUST meet all of the following criteria:

Document Properties

It MUST meet the conformance constraints for XML documents defined in XML Conformance [[!EPUB32]].

It MUST conform to all content conformance constraints expressed in Package Document Definition.

Some of the content conformance constraints can be checked by validating content documents against the schemas provided in Appendix A, Package Document Schema.

File Properties

The Package Document filename SHOULD use the file extension .opf.

Package Documents have the MIME media type application/oebps-package+xml [[!RFC4839]].

Reading System Conformance

An EPUB Reading System MUST meet all of the following criteria:

Processing

It MUST process the Package Document in conformance with all Reading System conformance constraints expressed in Package Document Definition.

It SHOULD process rendering metadata, as expressed in Package Rendering Metadata.

It MUST process fixed layout metadata, as expressed in Fixed-Layout Properties.

It MUST ignore proprietary metadata properties that pertain to layout expressions if they conflict behaviorally with the property semantics defined in Fixed-Layout Properties.

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.

When an element defined in this section has mandatory text content, that content is referred to as the value of the element in the explanatory descriptions.

The package Element

The package element is the root element of the Package Document and defines various aspects of the EPUB Package (see the introduction for a general overview).

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 Package conforms. The attribute MUST have the value "3.0" to indicate compliance with this version of the specification.

The unique-identifier attribute takes an IDREF [[!XML]] that identifies the dc:identifier element that provides the preferred, or primary, identifier. Refer to Publication Identifiers for more information.

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

Shared Attributes

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

dir

Specifies the base text direction of the content and attribute values of the carrying element and its descendants.

Inherent directionality specified using [[!Unicode]] takes precedence over this attribute.

Allowed values are ltr (left-to-right) and rtl (right-to-left).

<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

An absolute or relative IRI reference [[!RFC3987]] to 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 that can be used with the attribute.

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

Allowed on: item, itemref and link.

refines

Identifies the expression or resource augmented by the element. The value of the attribute must be a relative IRI [[!RFC3987]] referencing the resource or element being described.

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

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]].

<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.

Metadata

The metadata Element

The metadata element encapsulates meta information for the given Rendition.

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 Rendition's content (e.g., fixed-layout properties).

The Package Document is not designed to provide complex metadata encoding capabilities. If more detailed information about an EPUB Publication is needed, metadata records (e.g., that conform to an international standard such as [[!ONIX]] or are created for custom purposes) can be associated using the link element. This approach allows the metadata to be processed 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 include the [[!DC11]] 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. It is typically used to include rendering metadata defined in EPUB specifications, but MAY be used for any metadata purposes.

See [[EPUBAccessibility]] for accessibility metadata recommendations.

DCMES Required Elements

The identifier Element

The [[!DC11]] identifier element contains an identifier associated with the given Rendition, 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 [optional]

Content Model

Text

The metadata section MUST include an identifier element that contains an unambiguous identifier for the Rendition. This identifier MUST be marked as the Unique Identifier via the package element unique-identifier attribute.

The Unique Identifier for each Rendition MAY differ, and a Rendition MAY include additional identifier elements.

To differentiate different versions of the same EPUB Publication, this specification makes a distinction between the Unique Identifier for an EPUB Publication and the Release Identifier that uniquely identifies a specific version of it.

To identify a specific version of a packaged EPUB Publication, a Release Identifier can be constructed by combining the Unique Identifier with the last modified date of the Rendition. For more information on the semantics and requirements of the Release Identifier, refer to Release Identifier.

Whenever a Rendition is modified, it MUST include a new last modified date.

To determine whether an identifier conforms to an established system or has been granted by an issuing authority, Reading Systems SHOULD attempt to parse the value of the element.

For additional precision (e.g., if the scheme cannot be determined from the value or could lead to an ambiguous result), Authors MAY attach an identifier-type property to assist in Reading System identification.

When included, the identifier-type value SHOULD take precedence over value parsing the identifier. This specification does not require or endorse the use of any particular scheme for identifiers.

Reading Systems MUST trim all leading and trailing white space from the element value, as defined by the XML specification [[!XML]], before processing the value.

This specification imposes no additional restrictions or the requirements of the identifier except that it MUST be at least one character in length after white space has been trimmed. It is strongly encouraged that the identifier be a fully qualified URI, however.

The title Element

The [[!DC11]] title element represents an instance of a name given to 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 include at least one title element containing the title for the EPUB Publication.

Reading Systems MUST recognize the first title element in document order as the main title of the EPUB Publication (i.e., the primary one to present to users). This specification does not define how to process additional title elements.

The title for each Rendition MAY differ.

Reading Systems MUST trim all leading and trailing white space from the element value, as defined by the XML specification [[!XML]], before processing the value.

This specification imposes no additional restrictions or requirements on the title except that it MUST be at least one character in length after white space has been trimmed.

The language Element

The [[!DC11]] language element specifies the language of the content of the given Rendition. This value is not inherited by the individual resources of the Rendition.

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 include at least one language element with a value conforming to [[!BCP47]].

Additional language elements MAY be included for multilingual Publications, but each element's value MUST conform to [[!BCP47]]. The first language element in document order is considered the primary language of the rendition.

Languages for each Rendition MAY differ.

Reading Systems MUST trim all leading and trailing white space from the element value, as defined by the XML specification [[!XML]], before processing the value.

DCMES Optional Elements

General Definition

With the exception of identifier, language and title, all other [[!DC11]] elements 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

The OPTIONAL [[!DC11]] metadata for each Rendition MAY differ.

Reading Systems MUST trim all leading and trailing white space from the element value, as defined by the XML specification [[!XML]], before processing the value.

The value of all OPTIONAL [[!DC11]] elements MUST be at least one character in length after white space has been trimmed.

This specification does not modify the [[!DC11]] element definitions except as noted in the following sections.

The contributor Element

The [[!DC11]] contributor element is used to represent the name of a person, organization, etc. that played a secondary role in the creation of the content of an EPUB Publication.

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

The creator Element

The [[!DC11]] creator element represents the name of a person, organization, etc. responsible for the creation of the content of the Rendition. The role property can be attached to the element to indicate the function the creator played in the creation of the content.

The creator element SHOULD contain the name of the creator as a Reading System will present it to a user. The file-as property MAY be attached to include a normalized form of the name, and the alternate-script property to represent a creator's name in another language or script.

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

When determining display priority, Reading Systems MUST use the document order of creator elements in the metadata section, where the first creator element encountered is the primary creator. If a Reading System exposes creator metadata to the user, it SHOULD include all the creators listed in the metadata section whenever possible (e.g., when not constrained by display considerations).

Secondary contributors SHOULD be represented using the contributor element.

The date Element

The [[!DC11]] 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 Rendition was changed).

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.

Additional dates SHOULD be expressed using the specialized date properties available in the [[!DCTERMS]] vocabulary, or similar.

The publication date MAY be common to all instances of an EPUB Publication or MAY change from instance to instance (e.g., if the EPUB Publication gets generated on demand).

Only one date element is allowed.

The subject Element

The [[!DC11]] subject element identifies the subject of the EPUB Publication. The value of the element SHOULD be the human-readable heading or label, but MAY be the code value if the subject taxonomy does not provide a separate descriptive label.

Authors MAY identify the system or scheme the element's value is drawn from using the authority property.

When a scheme is identified, a subject code MUST be attached using the term property.

The term property MUST NOT be attached to 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 [[!DC11]] type element is used to indicate that the given EPUB Publication is of a specialized type (e.g., annotations or a dictionary packaged in EPUB format).

An informative registry of specialized EPUB Publication types for use with this element is maintained in the [[TypesRegistry]], but Authors MAY use any text string as a value.

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 being made in the expression, and the text content of the element represents the assertion. (Refer to Vocabulary Association Mechanisms for more information.)

This specification defines two types of metadata expressions that can be defined 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 enhances the meaning of the expression or resource referenced in its refines attribute. 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.

Subexpressions are not limited to refining only primary expressions and resources; they may be used to refine the meaning of other subexpressions, thereby creating chains of information.

All of the DCMES [[!DC11]] elements represent primary expressions, and permit refinement by meta element subexpressions.

This specification reserves the Meta Properties Vocabulary for use with the property attribute. Terms from other vocabularies MAY be used provided they have a prefix (refer to Reserved Prefixes for a list of prefixes that do not have to be declared).

The scheme attribute identifies the system or scheme that the element's value is drawn from. The value of the attribute MUST be a property data type that resolves to the resource that defines the scheme. If a Reading System does not recognize the scheme attribute value, it SHOULD treat the value of the element as a string.

Reading Systems SHOULD ignore all meta elements whose property attributes define expressions they do not recognize. A Reading System MUST NOT fail when encountering unknown expressions.

Unless an individual property explicitly defines a different white space normalization algorithm, Reading Systems MUST trim all leading and trailing white space from the meta element values, as defined by the XML specification [[!XML]], before further processing them.

Every meta element MUST express a value that is at least one character in length after white space normalization.

Manifest

The manifest Element

The manifest element provides an exhaustive list of the Publication Resources that constitute the given Rendition, each represented by an item element.

Element name

manifest

Usage

REQUIRED second child of package, following metadata.

Attributes

id [optional]

Content Model

item [1 or more]

This specification supports internationalized resource naming, so elements and attributes that reference Publication Resources accept IRIs as their value. For compatibility with older Reading Systems that only accept URIs, resource names need to be restricted 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 in the manifest identifies a Publication Resource by the IRI [[!RFC3987]] provided in its href attribute. The IRI MAY be absolute or relative. In the case of relative IRIs, Reading Systems MUST use the IRI of the Package Document as the base when resolving these to absolute IRIs. The resulting absolute IRI MUST be unique within the manifest scope.

All Publication Resources MUST be referenced from the manifest, regardless of whether they are Local or Remote Resources. Refer to Publication Resource Locations [[!EPUB32]] for media type-specific requirements regarding resource locations.

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

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. Core Media Type Resources MUST use the media type designated in Supported Media Types [[!EPUB32]].

The fallback attribute takes an IDREF [[!XML]] that identifies a fallback for the Publication Resource referenced from the item element. Fallbacks MAY be provided for Core Media Type Resources (e.g., to provide a static alternative to a Scripted Content Document). Fallback requirements for Foreign Resources are defined in Manifest Fallbacks.

This specification reserves the EPUB Manifest Properties Vocabulary for use with the properties attribute. Terms from other vocabularies MAY be used provided they have a prefix (refer to Reserved Prefixes for a list of prefixes that do not have to be declared).

Authors MUST declare all applicable descriptive metadata properties for each Publication Resource in this attribute, as Reading Systems MAY optimize the rendering depending on the properties that have been set (e.g., disable a rendering process or use a fallback). Reading Systems MUST ignore all descriptive metadata properties that they do not recognize.

Exactly one item MUST be declared 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 Packaging [[!MediaOverlays32]] for more information.

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

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

Foreign Resources MAY be referenced 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). Manifest fallbacks MUST be provided in such cases.

Manifest fallbacks are provided using the fallback attribute on the manifest item element that represents the 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 can be reached 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 Author's preferred fallback order.

A Reading System that does not support the Media Type of a given Publication Resource MUST traverse the fallback chain until it has identified at least one supported Publication Resource to be used in place of the unsupported resource. If the Reading System supports multiple Publication Resources in the fallback chain, it MAY select the resource to use based on specific properties of that resource, otherwise it SHOULD honor the Author's preferred fallback order. If a Reading System does not support any resource in the fallback chain, it MUST alert the reader that content could not be displayed.

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

  • For Foreign Resources referenced directly from spine itemref elements, the chain MUST contain at least one EPUB Content Document.

  • For Foreign Resources for which an intrinsic fallback cannot be provided, the chain MUST contain at least one Core Media Type Resource.

Fallback chains MUST NOT contain any circular- or self-references to item elements in the chain. User agents MUST terminate the fallback chain at the first reference to a manifest item that has already been encountered.

Fallbacks MAY also be provided for Top-Level Content Documents that are EPUB Content Documents; a Reading System MAY choose to utilize such fallbacks in order to find the optimal version of a Content Document to render in a given context. An example of when this feature can be utilized is when providing fallbacks for scripted content [[!ContentDocs32]].

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 [[!Publications301]] for more information about this element.

Spine

The spine Element

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

Element name

spine

Usage

REQUIRED third child of package, following manifest.

Attributes
Content Model

itemref [1 or more]

Reading Systems MUST provide a means of rendering the Rendition in the order defined in the spine, which includes: 1) recognizing the first primary itemref as the beginning of the default reading order; and, 2) rendering successive primary items in the order given in the spine.

All Publication Resources that are hyperlinked to from Publication Resources in the spine MUST themselves be listed in the spine, where hyperlinking is defined to be 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., all Publication Resources hyperlinked from hyperlinked Publication Resources also have to be listed, and so on.).

All Publication Resources hyperlinked to from the EPUB Navigation Document also MUST be listed in the spine, regardless of whether the Navigation Document is itself listed 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) do not have to 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 the default value is specified, the Author is expressing no preference and the Reading System can choose the rendering direction. The default value MUST be assumed when the attribute is not specified. In this case, the reading system SHOULD choose a default page-progression-direction value based on the first language element.

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 MAY also provide mechanisms to override the default direction (e.g., buttons or settings that allow the application of alternate style sheets).

Reading Systems MUST ignore the page progression direction defined in pre-paginated XHTML Content Documents. The page-progression-direction attribute defines the flow direction from one fixed-layout page to the next.

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

The itemref Element

The child itemref elements of the spine represent a sequential list of Publication Resources (typically EPUB Content Documents). The order of the itemref elements defines the default reading order of the given Rendition.

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 have to include 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 has to be read sequentially ("yes") or auxiliary content that enhances or augments the primary content and can be accessed 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 needs to access as part of the default reading order from supplementary content which might, for example, be presented in a popup window or omitted from an aural rendering.

When rendering an EPUB Publication, a Reading System MAY either suppress non-linear content so that it does not appear in the default reading order, or ignore the linear attribute in order to provide users access to the entire content of the EPUB Publication. This specification does not mandate which model Reading Systems have to use. A Reading System MAY also provide the option for users to toggle between the two models.

Each Rendition MUST include at least one itemref whose linear attribute value is either explicitly or implicitly set to "yes". An itemref that omits the linear attribute is assumed to have the value "yes".

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

This specification reserves the EPUB Spine Properties Vocabulary for use with the properties attribute. Terms from any other vocabulary MAY be used provided they have a prefix (refer to Reserved Prefixes for a list of prefixes that do not have to be declared).

All applicable descriptive metadata properties defined in the Spine Properties Vocabulary SHOULD be declared.

Reading Systems MUST ignore all metadata properties expressed in the properties attribute that they do not recognize.

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 resources to be assembled into logical groups for a variety of potential uses: enabling content that has been split across multiple EPUB Content Documents to be reassembled back into a meaningful unit (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 given Rendition.

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 within a Rendition, 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. The role of each collection element in the Package Document MUST be identified in its role attribute, whose value MUST be one or more NMTOKENs [[!XMLSCHEMA-2]] and/or absolute IRIs [[!RFC3987]]. The use of NMTOKEN values is reserved for roles not defined in EPUB, which are maintained in the [[!RoleRegistry]]. NMTOKEN values not defined in the registry are not valid. No roles are defined in this section.

Third parties MAY define custom roles for the collection element, but such roles MUST be identified using absolute IRIs. Custom roles MUST NOT incorporate the string "idpf.org" in the host component of their identifying IRI.

To facilitate interoperability of custom roles across Reading Systems, implementers are strongly encouraged to document their use of the collection element in [[RoleExtensions]].

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

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).

  • The refines attribute MUST NOT be attached.

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.

In the context of this specification, support for collections in Reading Systems is OPTIONAL. Reading Systems MUST ignore collection elements that define unrecognized roles.

The rendering of a Rendition 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.

Examples

Legacy

The meta Element

The meta element [[!OPF2]] is a legacy feature that previously provided a means of including generic metadata. It is replaced in EPUB 3 by the updated meta element, which uses different attributes and requires text content.

For more information about the meta element, refer to its definition in [[!OPF2]].

The guide Element

The guide element [[!OPF2]] is a legacy feature that previously provided machine-processable navigation to key structures in an EPUB Publication. It is replaced in EPUB 3 by landmarks in the EPUB Navigation Document.

For more information about the guide element, refer to its definition in [[!OPF2]].

NCX

The NCX [[!OPF2]] is a legacy feature that previously provided the table of contents for EPUB Publications. It is replaced in EPUB 3 by the EPUB Navigation Document.

For more information about the NCX, refer to its definition in [[!OPF2]].

Package Metadata

Publication Identifiers

Unique Identifier

The Author is responsible for including a primary identifier in the Package Document metadata that is unique to one and only one EPUB Publication. This Unique Identifier, whether chosen or assigned, MUST be stored in the dc:identifier element and be referenced as the Unique Identifier in the package element unique-identifier attribute.

Although not static, changes to the Unique Identifier for an EPUB Publication SHOULD be made as infrequently as possible. New identifiers SHOULD NOT be issued when updating metadata, fixing errata or making other minor changes to the EPUB Publication.

Reading Systems MUST NOT depend on the Unique Identifier being unique to one and only one EPUB Publication. Determining whether two EPUB Publications with the same Unique Identifier represent different versions of the same publication (see Release Identifier), or different publications, might require inspecting other metadata, such as the titles or authors.

Release Identifier

The Unique Identifier of an EPUB Publication typically SHOULD NOT change with each minor revision to the package or its contents, as Unique Identifiers are intended to have maximal persistence both for referencing and distribution purposes. Each release of an EPUB Publication normally requires that the new version be uniquely identifiable, however, which results in the contradictory need for reliable Unique Identifiers that are changeable.

To redress this problem of identifying minor modifications and releases without changing the Unique Identifier, this specification defines the semantics for a Release Identifier, or means of distinguishing and sequentially ordering EPUB Publications with the same Unique Identifier.

The Release Identifier is not an actual property in the package metadata section, but is a value that can be obtained from two other mandatory pieces of metadata: the Unique Identifier and the last modification date of the Rendition. When the taken together, the combined value represents a unique identity that can be used to distinguish any particular version of an EPUB Publication from another.

To ensure that a Release Identifier can be constructed, each Rendition MUST include exactly one [[!DCTERMS]] modified property containing its last modification date. The value of this property MUST be an [[!XMLSCHEMA-2]] dateTime conformant date of the form:

CCYY-MM-DDThh:mm:ssZ

The last modification date MUST be expressed in Coordinated Universal Time (UTC) and MUST be terminated by the "Z" (Zulu) time zone indicator.

Additional modified properties MAY be included in the package metadata, but they MUST have a different subject (i.e., they require a refines attribute that references an element or resource).

Although not a part of the package metadata, for referencing and other purposes all string representations of the identifier MUST be constructed using the at sign (@) as the separator (i.e., of the form "id@date"). Whitespace MUST NOT be included when concatenating the strings.

Note that it is possible that the separator character MAY occur in the Unique Identifier, as these identifiers MAY be any string value. The Release Identifier consequently MUST be split on the last instance of the at sign when decomposing it into its component parts.

The Release Identifier does not supersede the Unique Identifier, but represents the means by which different versions of the same EPUB Publication can be distinguished and identified in distribution channels and by Reading Systems. The sequential, chronological order inherent in the format of the timestamp also places EPUB Publications in order without requiring knowledge of the exact identifier that came before.

The Release Identifier consequently allows a set of EPUB Publications to be inspected to determine if they represent the same version of the same Publication, different versions of a single EPUB Publication, or any combination of differing and similar EPUB Publications.

When an EPUB Container includes more than one Rendition of an EPUB Publication, updating the last modified date of the default rendition for each release — even if it has not been updated — will help ensure that the EPUB Publication does not appear to be the same version as an earlier release, as Reading Systems only have to process the default rendition.

Vocabulary Association Mechanisms

Introduction

The property, properties, rel and scheme attributes use the property data type to represent terms from metadata vocabularies. Similar to a CURIE [[RDFA-CORE]], the property data type represents an IRI [[RFC3987]] in compact form and simplifies the authoring of metadata from standardized vocabularies.

A property value is an expression that consists of a prefix and a reference, where the prefix — whether literal or implied — is a shorthand mapping of an IRI that typically resolves to a term vocabulary. When the prefix is converted to its IRI representation and combined with the reference, the resulting IRI normally resolves to a fragment within that vocabulary that contains human- and/or machine-readable information about the term.

To assist Reading Systems in processing property values, this specification defines three mechanisms to establish the IRI a prefix maps to:

  • default vocabularies — define the mapping when a property value does not include a prefix;

  • reserved prefixes — these mappings are predefined (i.e., all Reading Systems recognize them) and can be used without having to be declared; and

  • the prefix attribute — a declarative means of creating new prefix mappings on the root package element.

Default Vocabularies

A default vocabulary is a vocabulary that does not require a prefix to be declared in order to use its terms, and whose terms MUST always be unprefixed.

As the Package Document has multiple unrelated uses for metadata terms, a single default vocabulary is not defined for all attributes. Instead, different default vocabularies are defined for use in attributes that accept a property data type as follows:

  • The Meta Properties Vocabulary is defined to be the default vocabulary for the meta property attribute.

    If the attribute's value does not include a prefix, the following IRI [[!RFC3987]] stem MUST be used to generate the resulting IRI: http://idpf.org/epub/vocab/package/meta/#

  • The Metadata Link Vocabulary is defined to be the default vocabulary for the link rel and properties attributes.

    If any of these attributes' values do not include a prefix, the following IRI [[!RFC3987]] stem MUST be used to generate the resulting IRI for them: http://idpf.org/epub/vocab/package/link/#

  • The Manifest Properties Vocabulary is defined to be the default vocabulary for the item properties attribute.

    If any of the attribute's values do not include a prefix, the following IRI [[!RFC3987]] stem MUST be used to generate the resulting IRI for them: http://idpf.org/epub/vocab/package/item/#

  • The Spine Properties Vocabulary is defined to be the default vocabulary for the itemref properties attribute.

    If any of the attribute's values do not include a prefix, the following IRI [[!RFC3987]] stem MUST be used to generate the resulting IRI for them: http://idpf.org/epub/vocab/package/itemref/#

The IRIs associated with these vocabularies MUST NOT be assigned a prefix using the prefix attribute.

Reserved Prefixes

This specification reserves the following set of prefixes that Authors MAY use in package metadata without having to declare.

Although reserved prefixes are an authoring convenience, reliance on them can lead to interoperability issues. Validation tools will often reject new prefixes until the tools are updated, for example. Authors are strongly encouraged to declare all prefixes they use to avoid such issues.

Prefix IRI
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#

Reading Systems MUST resolve all reserved prefixes used in Package Documents using their predefined URIs unless a local prefix is declared. Reserved prefixes SHOULD NOT be overridden in the prefix attribute, but Reading Systems MUST use such local overrides when encountered.

As changes to the reserved prefixes and updates to Reading Systems are not always going happen in synchrony, Reading Systems MUST NOT fail when encountering unrecognized prefixes (i.e., not reserved and not declared using the prefix attribute).

The prefix Attribute

The prefix attribute defines additional prefix mappings not reserved by this specification.

The value of the prefix attribute is a white space-separated list of one or more prefix-to-IRI 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) ;  

To avoid conflicts, the prefix attribute MUST NOT be used to declare a prefix that maps to the default vocabulary. If the prefix attribute includes a declaration for a predefined prefix, Reading Systems MUST use the URI mapping defined in the prefix attribute, regardless of whether of it maps to the same URI as the predefined prefix.

The prefix '_' MUST NOT be declared as it is reserved for future compatibility with RDFa [[!RDFA-CORE]] processing.

For future compatibility with alternative serializations of the Package Document, a prefix for the Dublin Core /elements/1.1/ namespace [[!DCTERMS]] MUST NOT be declared in the prefix attribute. Authors MUST use only the [[!DC11]] elements allowed in the Package Document metadata.

The property Data Type

Syntax

The property data type is a compact means of expressing an IRI [[!RFC3987]] 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 = ? irelative-ref ? ; /* as defined in [[!RFC3987]] */

The property data type is derived from the CURIE data type defined in [[!RDFA-CORE]], and represents a subset of CURIEs.

After processing, this property would expand to the following IRI:

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

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

When a prefix is omitted 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.

Processing

A Reading System MUST use the following rules to create an IRI [[!RFC3987]] from a property:

  • If the property consists only of a reference, the IRI is obtained by concatenating the IRI stem associated with the default vocabulary to the reference.

  • If the property consists of a prefix and reference, the IRI is obtained by concatenating the IRI stem associated with the prefix to the reference. If no matching prefix has been defined, the property is invalid and MUST be ignored.

The resulting IRI MUST be valid to [[!RFC3987]]. Reading Systems do not have to resolve this IRI, however.

Package Rendering Metadata

Introduction

Not all rendering information can be expressed through the underlying technologies that EPUB is built upon. For example, although HTML with CSS provides powerful layout capabilities, those capabilities are limited to the scope of the document being rendered.

This section defines general-purpose properties that allow Authors to express package-level rendering intentions (i.e., functionality that can only be implemented by the EPUB Reading System). If a Reading System supports the desired rendering, these properties enable the user to be presented the content as the Author optimally designed it.

Referencing

The base IRI for referencing these properties is http://www.idpf.org/vocab/rendition/#.

The "rendition:" prefix is reserved for use with the package rendering properties and does not have to be declared in the Package Document.

General Properties

The rendition:flow Property

The rendition:flow property specifies the Author preference for how Reading Systems should handle content overflow.

Usage

When the rendition:flow property is specified on a meta element, it indicates the Author's global preference for overflow content handling (i.e., for all spine items). Authors MAY indicate a preference for dynamic pagination or scrolling. For scrolled content, it is also possible to specify whether consecutive EPUB Content Documents are to be rendered as a continuous scrolling view or whether each is to be rendered separately (i.e., with a dynamic page break between each).

If a Reading System supports the specified rendering, it SHOULD use that method to handle overflow content, but MAY provide the option for users to override the requested rendering.

The default value auto MUST be assumed by Reading Systems as the global value if no meta element carrying this property occurs in the metadata section. Reading Systems MAY support only this default value.

If a Reading Systems supports the rendition:layout property, it MUST ignore the rendition:flow property when it has been set on a spine item that also specifies the rendition:layout value pre-paginated.

Note that when two reflowable EPUB Content Documents occur sequentially in the spine, the default rendering for their [[!HTML]] body elements is consistent with the page-break-before property [[!CSSSnapshot]] having been set to always. In addition to using the rendition:flow property, Authors MAY override this behavior through an appropriate style sheet declaration, if the Reading System supports such overrides.

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

Allowed Values

The following values are defined for use with the rendition:flow property:

paginated

The Reading System SHOULD dynamically paginate all overflow content.

scrolled-continuous

The Reading System SHOULD render all Content Documents such that overflow content is scrollable, and the EPUB Publication represented by the given Rendition SHOULD be presented as one continuous scroll from spine item to spine item (except where locally overridden).

Note that Authors SHOULD NOT create publications in which different resources have different block flow directions, as continuous scrolled rendition in EPUB Reading Systems would be problematic.

scrolled-doc

The Reading System SHOULD render all Content Documents such that overflow content is scrollable, and each spine item SHOULD be presented as a separate scrollable document.

auto

The Author does not have a preference for overflow handling. The Reading System MAY render overflow content using its default method or a user preference, whichever is applicable.

Spine Overrides

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

flow-auto
Indicates no preference for overflow content handling by the Author.
flow-paginated
Indicates the Author preference is to dynamically paginate content overflow.
flow-scrolled-continuous
Indicates the Author preference is to provide a scrolled view for overflow content, and that consecutive spine items with this property are to be rendered as a continuous scroll.
flow-scrolled-doc
Indicates the Author preference is to provide a scrolled view for overflow content, and each spine item with this property is to be rendered as a separate scrollable document.

Only one of these overrides is allowed on any given spine item.

For the rendition:flow-scrolled-continuous property, the scroll direction is defined relative to the block flow direction of the root element of the XHTML Content Document referenced by the itemref element. The scroll direction is vertical if the block flow direction is downward (top-to-bottom). It is horizontal if the block flow direction of the root element is rightward (left-to-right) or leftward (right-to-left).

Examples

The rendition:align-x-center Property

The rendition:align-x-center property specifies that the given spine item should be centered horizontally in the viewport or spread.

When the rendition:align-x-center property is set on a spine item, it indicates that the rendered content SHOULD be centered horizontally within the Viewport or spread, as applicable. This property does not affect the rendering of the spine item, only the placement of the resulting content box.

For reflowable content, Reading Systems that support this property MUST center each virtual page.

This version of this specification does not define a default rendering behavior when this property is not supported or specified. Reading Systems MAY render spine items by their own design.

This property was developed primarily to handle "Naka-Tobira (中扉)" (sectional title pages), in the absence of reliable centering control within the content rendering. As support for paged media evolves in CSS, however, this property is expected to be deprecated. Authors are encouraged to use CSS solutions when effective.

Fixed-Layout Properties

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." [[EPUB3Overview]]

But this principle doesn’t work for all types of documents. Sometimes content and design are so intertwined they cannot be separated. Any change in appearance risks changing the meaning, or losing all meaning. Fixed-Layout Documents give Authors greater control over presentation when a reflowable EPUB is not suitable for the content.

This section defines a set of metadata properties to allow declarative expression of intended rendering behaviors of Fixed-Layout Documents in the context of EPUB 3.

EPUB 3 affords multiple mechanisms for representing fixed-layout content. When fixed-layout content is necessary, the Author'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 Author's choice of mechanism.

The rendition:layout Property

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

Usage

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

The default value reflowable MUST be assumed by EPUB Reading Systems as the global value if no meta element carrying this property occurs in the metadata section.

When the rendition:layout property is set to pre-paginated, Reading Systems MUST NOT include space between the adjacent content slots when rendering Synthetic Spreads.

When the property is set to pre-paginated for a spine item, its content dimensions MUST be set as defined in Fixed Layouts [[!ContentDocs32]].

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

Allowed Values

The following values are defined for use with the rendition:layout property:

reflowable

The given Rendition is not pre-paginated. Reading Systems MAY apply dynamic pagination when rendering.

pre-paginated

The given Rendition is pre-paginated. Reading Systems MUST 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, since, as a result of intrinsic properties of such documents, dynamic style changes are highly likely to have unintended consequences. Authors need to take into account 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.

Spine Overrides

Authors 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.

Only one of these overrides is allowed on any given spine item.

Examples

The rendition:orientation Property

The rendition:orientation property specifies which orientation the Author intends the given Rendition to be rendered in.

Usage

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

The default value auto MUST be assumed by Reading Systems as the global value if no meta element carrying this property occurs in the metadata section.

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

Allowed Values

The following values are defined for use with the rendition:orientation property:

landscape

The given Rendition is intended for landscape rendering.

portrait

The given Rendition is intended for portrait rendering.

auto

The given Rendition is not orientation constrained.

Reading Systems that support multiple orientations SHOULD convey the intended orientation to the user, unless the given value is auto. The means by which the intent is conveyed is implementation-specific.

Spine Overrides

Authors 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 the given spine item is to be rendered in landscape orientation.
orientation-portrait
Specifies that the given spine item is to be rendered in portrait orientation.

Only one of these overrides is allowed on any given spine item.

Examples

The rendition:spread Property

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

Usage

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

The default value auto MUST be assumed by Reading Systems as the global value if no meta element carrying this property occurs in the metadata section.

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

Allowed Values

The following values are defined for use with the rendition:spread property:

none

Reading Systems MUST NOT incorporate spine items in a Synthetic Spread.

landscape

Reading Systems SHOULD 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.

Authors are advised to use the value "both" instead, as spreads that are readable in portrait orientation are also readable in landscape. Reading Systems SHOULD treat the value "portrait" as a synonym of "both" and create spreads regardless of orientation.

both

Reading Systems SHOULD render a Synthetic Spread regardless of device orientation.

auto

No explicit Synthetic Spread behavior is defined. Reading Systems MAY use Synthetic Spreads in specific or all device orientations as part of a Content Display Area utilization optimization process.

When Synthetic Spreads are used in the context of HTML and SVG Content Documents, the dimensions given via the viewport meta element [[ContentDocs32]] and viewBox attribute [[ContentDocs32]] 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.

Spine Overrides

Authors 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 [[!Publications301]] for more information.

Only one of these overrides is allowed on any given spine item.

Examples

The rendition:page-spread-* Properties

Usage

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 Author MAY override this automatic population behavior and forcing a document to be placed 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 SHOULD be rendered in the left-hand slot in the spread, and rendition:page-spread-right that it SHOULD be rendered in the right-hand slot. The rendition:page-spread-center property indicates that the synthetic spread mode SHOULD be overridden and a single viewport rendered and 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.

The rendition:page-spread-* properties take precedence over whatever value of the page-break-before property [[!CSSSnapshot]] has been set for an XHTML Content Document.

The presence of rendition:page-spread-center does not change the viewport dimensions. In particular, it does not indicate that a viewport with the size of the whole spread has to be created. This is important so that the scale factor stays consistent between regular and center-spread pages.

When a reflowable spine item follows a pre-paginated one, the reflowable one SHOULD start on the next page (as defined by the page-progression-direction) when it lacks a rendition:page-spread-* property value. If the reflowable spine item has a rendition:page-spread-* specification, it MUST be honored (e.g., by inserting a blank page).

Similarly, when a pre-paginated spine item follows a reflowable one, the pre-paginated one SHOULD start on the next page (as defined by the page-progression-direction) when it lacks a rendition:page-spread-* property value. If the pre-paginated spine item has a rendition:page-spread-* specification, it MUST be honored (e.g., by inserting a blank page).

Although Authors often indicate to use a spread in certain device orientations, the content itself does not represent true spreads (i.e., two consecutive pages that have to be rendered side-by-side for readability, such as a two-page map). To indicate that two consecutive pages represent a true spread, Authors 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. When a Reading System encounters two spine items that represent a true spread, it SHOULD create the spread with no space between the adjacent pages.

Only one page-spread-* property can be declared 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. Authors can use either property set, but older Reading Systems might only recognize the unprefixed versions. The EPUB Spine Properties Vocabulary is no longer being extended for package rendering metadata, so an unprefixed page-spread-center is not available.

Examples

The rendition:viewport Property (Deprecated)

The rendition:viewport property allows Authors to express the CSS initial containing block (ICB) [[!CSS21]] 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 [[!Publications301]] for more information.

EPUB Navigation Document

Introduction

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

The EPUB Navigation Document is an XHTML Content Document, but with additional restrictions on its structure to facilitate the machine-processing of its contents. [[HTML]] nav elements contain the specialized navigational information, which remains human-readable as well as allowing Reading Systems to generate navigational interfaces.

But the EPUB Navigation Document is not exclusively for machine processing. Because it is an XHTML Content Document, it can be part of the linear reading order, avoiding the need for duplicate tables of contents. Content which is only destined for machine processing, such as page lists, can be hidden from visual rendering with the hidden attribute.

Note that Reading Systems might strip scripting, styling, and HTML formatting as they generate navigational interfaces from information found in the EPUB Navigation Document. If such formatting and functionality is needed, then the EPUB Navigation Document also needs to be included in the spine. The use of progressive enhancement [[ContentDocs32]] 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.

Content Conformance

A conformant EPUB Navigation Document MUST meet all of the following criteria:

Document Properties

It MUST conform to the content conformance constraints for XHTML Content Documents defined in XHTML Content Documents — Content Conformance [[!ContentDocs32]].

It MUST conform to the content conformance constraints specific to EPUB Navigation Documents defined in EPUB Navigation Document Definition.

As a conforming XHTML Content Document, it MAY be included in the spine.

Reading System Conformance

A conformant EPUB Reading System MUST meet all of the following criteria for processing EPUB Navigation Documents:

EPUB Navigation Document Definition

The nav Element: Restrictions

When a nav element carries the epub:type attribute [[!ContentDocs32]] 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 content model of the nav element is interpreted as follows:

  • 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, a large list of illustrations can be segmented 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. Although non-textual descendant elements MAY be rendered directly to users, text content included in title or alt attributes MUST be used when determining compliance with this requirement.

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

  • The IRI reference provided in the href attribute of the a element MUST adhere to the following requirements:

  • An a element MAY be followed by an ol ordered list representing a subsidiary content level below that heading (e.g., all the subsection headings of a section).

  • A span element MUST be followed by an ol ordered list; it cannot be used 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.

EPUB specifications MAY introduce further restrictions on the content model defined above for nav elements in the EPUB Navigation Document.

In the context of this specification, the default display style of list items within nav elements MUST be equivalent to the list-style: none property [[!CSSSnapshot]]. Reading Systems MUST NOT show list item numbering on these lists when presenting the Navigation Document outside of the spine, regardless of their support for CSS. Authors 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 [[ContentDocs32]].

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 has to be included 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 for the EPUB Publication.

landmarks

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

Additional navigation types can be included in the EPUB Navigation Document. See Other nav Elements for more information.

The toc nav Element

The toc nav element defines the primary navigational hierarchy of the given Rendition. 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).

The references in the toc nav element MUST be ordered 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 being represented by the EPUB Publication.

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

The page references within the page-list nav MUST be ordered so that they match both the order of the targeted EPUB Content Documents in the spine and the order of each page within its respective EPUB Content Document.

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

The destinations of the page-list references MAY be identified in their respective EPUB Content Documents using the pagebreak term [[!EPUB-SSV]].

The landmarks nav Element

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

The epub:type attribute [[!ContentDocs32]] 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 include one or more nav elements in addition to the toc, page-list and landmarks nav elements defined in the preceding sections. These additional nav elements SHOULD have an epub:type attribute to provide a machine-readable semantic, and MUST have a human-readable heading as their first child.

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

The hidden attribute

In some cases, Authors 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 usually is not rendered as part of the content flow but is instead exposed to the user separately in a dedicated navigation user interface.

While the display property [[!CSSSnapshot]] can be used to control 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, authors 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 navigation data is rendered outside of the content flow (such as in dedicated navigation user interfaces provided by Reading Systems).

Package Document Schema

A non-normative schema for Package Documents is available at https://w3c.github.io/publ-epub-revision/epub32/schema/package-32.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.

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 a Rendition of an EPUB Publication. It identifies the resources in the Rendition and provides metadata information. The Package Document and its related specifications are maintained and defined by the W3C’s EPUB 3 Community Group.

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 Packages 3.2 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 Packages 3.2 specification located at http://w3c.github.io/publ-epub-revision/epub32/spec/epub-packages.html.

The EPUB Packages 3.2 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. The following list of applications is not exhaustive.

  • Adobe Digital Editions

  • Aldiko

  • Azardi

  • Apple iBooks

  • Barnes & Noble Nook

  • Bluefire Reader

  • Calibre

  • Google Play Books

  • Kobo

  • Microsoft Edge

  • Readium

Additional information:
Magic number(s):

none

File extension(s):

.opf

Macintosh File Type Code(s):

TEXT

Fragment Identifiers:

A registry of linking schemes is maintained at http://www.idpf.org/epub/linking/. Some of these schemes define custom fragment identifiers that 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:

The published specification is a work product of the World Wide Web Consortium’s EPUB 3 Community Group. W3C has change control over this specification.