ISO/IEC TS 30135-3:2014
(Main)Information technology — Digital publishing — EPUB3 — Part 3: Content Documents
Information technology — Digital publishing — EPUB3 — Part 3: Content Documents
This specification, EPUB Content Documents 3.0, defines profiles of HTML5, SVG, and CSS for use in the context of EPUB® Publications. This specification is one of a family of related specifications that compose EPUB 3, the third major revision of 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: The EPUB 3 Overview [EPUB3Overview], which provides an informative overview of EPUB and a roadmap to the rest of the EPUB 3 documents. The Overview should be read first. EPUB Publications 3.0 [Publications30], which defines publication-level semantics and overarching conformance requirements for EPUB Publications. EPUB Open Container Format (OCF) 3.0 [OCF3], which defines a file format and processing model for encapsulating a set of related resources into a single-file (ZIP) EPUB Container. EPUB Media Overlays 3.0 [MediaOverlays30], which defines a format and a processing model for synchronization of text and audio. This specification supersedes Open Publication Structure (OPS) 2.0.1 [OPS2]. Refer to [EPUB3Changes] for information on differences between this specification and its predecessor.
Technologies de l'information — Publications numériques — EPUB3 — Partie 3: Documents de contenu
General Information
Relations
Standards Content (Sample)
TECHNICAL ISO/IEC
SPECIFICATION TS
30135-3
First edition
2014-11-15
Information technology — Digital
publishing — EPUB3 —
Part 3:
Content Documents
Technologies de l'information — Publications numériques — EPUB3 —
Partie 3: Documents de contenu
Reference number
ISO/IEC TS 30135-3:2014(E)
©
ISO/IEC 2014
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ISO/IEC TS 30135-3:2014(E)
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ii © ISO/IEC 2014 – All rights reserved
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ISO/IEC TS 30135-3:2014(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, the joint
technical committee may decide to publish an ISO/IEC Technical Specification (ISO/IEC TS), which
represents an agreement between the members of the joint technical committee and is accepted for
publication if it is approved by 2/3 of the members of the committee casting a vote.
An ISO/IEC TS is reviewed after three years in order to decide whether it will be confirmed for a further three
years, revised to become an International Standard, or withdrawn. If the ISO/IEC TS is confirmed, it is
reviewed again after a further three years, at which time it must either be transformed into an International
Standard or be withdrawn.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC TS 30135 series were prepared by Korean Agency for Technology and Standards (as KS X 6070
series) with International Digital Publishing Forum and were adopted, under a special “fast-track procedure”,
by Joint Technical Committee ISO/IEC JTC 1, Information technology, in parallel with its approval by the
national bodies of ISO and IEC.
ISO/IEC TS 30135 consists of the following parts, under the general title Information technology — Document
description and processing languages — EPUB 3:
— Part 1: Overview
— Part 2: Publications
— Part 3: Content Documents
— Part 4: Open Container Format
— Part 5: Media Overlay
— Part 6: Canonical Fragment Identifier
— Part 7: Fixed-Layout Documents
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EPUB Content Documents 3.0
Recommended Specification 11 October 2011
THIS VERSION
http://www.idpf.org/epub/30/spec/epub30-contentdocs-20111011.html
LATEST VERSION
http://www.idpf.org/epub/30/spec/epub30-contentdocs.html
PREVIOUS VERSION
http://www.idpf.org/epub/30/spec/epub30-contentdocs-20110908.html
A diff of changes from the previous draft is available at this link.
Please refer to the errata for this document, which may include some normative corrections.
Copyright © 2010, 2011 International Digital Publishing Forum™
All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and
dissemination of this work with changes is prohibited except with the written permission of the International
Digital Publishing Forum (IDPF).
EPUB is a registered trademark of the International Digital Publishing Forum.
Editors
Markus Gylling, DAISY Consortium
William McCoy, International Digital Publishing Forum (IDPF)
Elika J. Etemad, Invited Expert
Matt Garrish, Invited Expert
TAB LE O F CO NTENTS
1. Overview
1.1. Purpose and Scope
1.2. Relationship to Other Specifications
1.2.1. Relationship to HTML5
1.2.2. Relationship to SVG
1.2.3. Relationship to CSS
1.2.4. EPUB 3 Versioning Strategy
1.3. Terminology
1.4. Conformance Statements
1.5. Namespace prefix mappings
2. EPUB Content Documents
2.1. XHTML Content Documents
2.1.1. Content Conformance
2.1.2. Reading System Conformance
2.1.3. HTML5 Extensions and Enhancements
2.1.3.1. Semantic Inflection
2.1.3.1.1. Introduction
2.1.3.1.2. The epub:type Attribute
2.1.3.1.3. Vocabulary Association
2.1.3.1.4. Processing Requirements
2.1.3.2. SSML Attributes
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2.1.3.2.1. Overview
2.1.3.2.2. The ssml:ph attribute
2.1.3.2.3. The ssml:alphabet attribute
2.1.3.3. Content Switching
2.1.3.3.1. Introduction
2.1.3.3.2. Definition
2.1.3.3.2.1. The epub:switch Element
2.1.3.3.2.2. The epub:case Element
2.1.3.3.2.3. The epub:default Element
2.1.3.3.3. Processing
2.1.3.4. The epub:trigger Element
2.1.3.5. Alternate Style Tags
2.1.4. HTML5 Deviations and Constraints
2.1.4.1. Embedded MathML
2.1.4.1.1. Introduction
2.1.4.1.2. Content Conformance
2.1.4.1.3. Reading System Conformance
2.1.4.1.4. Alternative Content
2.1.4.2. Embedded SVG
2.1.4.2.1. Embedded SVG and CSS
2.1.4.3. Unicode Restrictions
2.1.4.4. Discouraged Constructs
2.2. EPUB Navigation Documents
2.2.1. Introduction
2.2.2. Content Conformance
2.2.3. Reading System Conformance
2.2.4. EPUB Navigation Document Definition
2.2.4.1. The nav Element: Restrictions
2.2.4.2. The nav Element: Types
2.2.4.2.1. The toc nav Element
2.2.4.2.2. The page-list nav Element
2.2.4.2.3. The landmarks nav Element
2.2.4.2.4. Other nav Elements
2.2.4.3. The hidden attribute
2.3. SVG Content Documents
2.3.1. Introduction
2.3.2. Content Conformance
2.3.3. Restrictions on SVG 1.1
2.3.4. Reading System Conformance
2.4. Scripted Content Documents
2.4.1. Scripting Contexts
2.4.2. Content Conformance
2.4.3. Reading System Conformance
2.4.4. Security Considerations
2.4.5. Event Model Considerations
3. EPUB Style Sheets
3.1. Content Conformance
3.2. Reading System Conformance
3.3. EPUB 3 CSS Profile
3.3.1. CSS 2.1
3.3.2. CSS 2.0
3.3.3. CSS 3.0 Speech
3.3.4. CSS Fonts Level 3
3.3.5. CSS Text Level 3
3.3.6. CSS Writing Modes
3.3.7. Media Queries
3.3.8. CSS Namespaces
3.3.9. CSS Multi-Column Layout
3.3.10. Ruby Positioning
3.3.11. Display Property Values oeb-page-head and oeb-page-foot
4. PLS Documents
4.1. Overview
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4.2. EPUB Publication Conformance
4.3. Content Conformance
4.4. Reading System Conformance
A. Schemas
A.1. XHTML Content Document Schema
A.2. EPUB Navigation Document Schema
A.3. SVG Content Document Schema
B. JavaScript epubReadingSystem Object
B.1. Syntax
B.2. Description
B.3. Properties
B.4. Methods
B.4.1. hasFeature
B.4.1.1. Syntax
B.4.1.2. Description
B.4.1.3. Features
C. Acknowledgements and Contributors
References
› 1 Overview
› 1.1 Purpose and Scope
This section is informative
This specification, EPUB Content Documents 3.0, defines profiles of HTML5, SVG, and CSS for use in
the context of EPUB® Publications.
This specification is one of a family of related specifications that compose EPUB 3, the third major
revision of 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:
The EPUB 3 Overview [EPUB3Overview], which provides an informative overview of EPUB and a
roadmap to the rest of the EPUB 3 documents. The Overview should be read first.
EPUB Publications 3.0 [Publications30], which defines publication-level semantics and
overarching conformance requirements for EPUB Publications.
EPUB Open Container Format (OCF) 3.0 [OCF3], which defines a file format and processing
model for encapsulating a set of related resources into a single-file (ZIP) EPUB Container.
EPUB Media Overlays 3.0 [MediaOverlays30], which defines a format and a processing model for
synchronization of text and audio.
This specification supersedes Open Publication Structure (OPS) 2.0.1 [OPS2]. Refer to
[EPUB3Changes] for information on differences between this specification and its predecessor.
› 1.2 Relationship to Other Specifications
This section is informative
› 1.2.1 Relationship to HTML5
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The XHTML document type defined by this specification is based on W3C [HTML5], and inherits all
definitions of semantics, structure and processing behaviors from the HTML5 specification unless
otherwise specified.
In addition, this specification defines a set of extensions to the W3C HTML5 document model that
Authors may include in XHTML Content Documents.
This specification defines a simplified processing model that does not require Reading Systems to
support scripting, HTML5 forms or the HTML5 DOM. EPUB Reading Systems conformant with this
specification are only required to be able to process a conforming EPUB Content Document. As support
for scripting and HTML5 forms are optional Reading System features, a conformant Reading System
might not be a fully-conformant HTML5 User Agent (i.e., it might not implement the complete HTML5
processing model).
› 1.2.2 Relationship to S VG
This specification defines a restricted subset of SVG 1.1 to represent vector graphics inline in XHTML
Content Documents and as standalone SVG Content Documents.
› 1.2.3 Relationship to CS S
The CSS profile defined in this specification has CSS 2.1 [CSS2.1] as its baseline. Any CSS Style Sheet
that conforms to CSS 2.1 may be used in the context of an EPUB Publication, except as noted in CSS
2.1.
This specification also incorporates features defined by CSS3 Modules and introduces EPUB-specific
CSS constructs.
1.2.4 EPUB 3 Versioning S trategy
›
EPUB 3 references W3C specifications that are not yet final, and incompatible changes to them may
occur in the future that would cause EPUB 3 Content Documents that were previously conformant to no
longer be conformant to the latest versions of the referenced specifications.
The IDPF anticipates revising the EPUB 3 specifications if and when such incompatible changes occur,
updating the normative constraints defined herein as necessary and incrementing the minor version
number of EPUB 3 (e.g., publishing an EPUB 3.0.n).
1.3 Terminology
›
EPUB Publication (or Publication)
A logical document entity consisting of a set of interrelated resources and packaged in an
EPUB Container, as defined by this specification and its sibling specifications.
Publication Resource
A resource that contains content or instructions that contribute to the logic and rendering of
the EPUB Publication. In the absence of this resource, the Publication might not render as
intended by the Author. Examples of Publication Resources include the Package Document,
EPUB Content Documents, EPUB Style Sheets, audio, video, images, embedded fonts and
scripts.
With the exception of the Package Document itself, Publication Resources must be listed in
the manifest [Publications30] and must be bundled in the EPUB container file unless
specified otherwise in Publication Resource Locations [Publications30].
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Examples of resources that are not Publication Resources include those identified by the
Package Document link [Publications30] element and those identified in outbound hyperlinks
that resolve outside the EPUB Container (e.g., referenced from an [HTML5] a element href
attribute).
Core Media Type Resource
A Publication Resource that is a Core Media Type and may therefore be included in the
EPUB Publication without the provision of fallbacks [Publications30].
EPUB Content Document
A Publication Resource that conforms to one of the EPUB Content Document definitions
(XHTML or SVG).
An EPUB Content Document is a Core Media Type, and may therefore be included in the
EPUB Publication without the provision of fallbacks [Publications30].
XHTML Content Document
An EPUB Content Document conforming to the profile of [HTML5] defined in XHTML Content
Documents.
XHTML Content Documents use the XHTML syntax of [HTML5].
SVG Content Document
An EPUB Content Document conforming to the constraints expressed in SVG Content
Documents.
EPUB Navigation Document
A specialization of the XHTML Content Document, containing human- and machine-readable
global navigation information, conforming to the constraints expressed in EPUB Navigation
Documents.
Scripted Content Document
An EPUB Content Document that includes scripting or an XHTML Content Document that
contains HTML5 forms elements.
Refer to Scripted Content Documents for more information.
Top-level Content Document
An EPUB Content Document referenced directly from the spine
Core Media Type
A set of Publication Resource types for which no fallback is required. Refer to Publication
Resources [Publications30] for more information.
Package Document
A Publication Resource carrying bibliographical and structural metadata about the EPUB
Publication, as defined in Package Documents [Publications30].
Manifest
A list of all Publication Resources that constitute the EPUB Publication.
Refer to manifest [Publications30] for more information.
Spine
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An ordered list of Publication Resources, typically EPUB Content Documents, representing
the default reading order of the Publication.
Refer to spine [Publications30] for more information.
Text-to-Speech (TTS)
The rendering of the textual content of an EPUB Publication as artificial human speech using
a synthesized voice.
EPUB Style Sheet (or Style Sheet)
A CSS Style Sheet conforming to the CSS profile defined in EPUB Style Sheets.
Viewport
The region of an EPUB Reading System in which the content of an EPUB Publication is
rendered visually to a User.
CSS Viewport
A Viewport capable of displaying CSS-styled content.
SVG Viewport
A Viewport capable of displaying SVG images.
EPUB Container (or Container)
The ZIP-based packaging and distribution format for EPUB Publications defined in [OCF3].
Author
The person(s) or organization responsible for the creation of an EPUB Publication, which is
not necessarily the creator of the content and resources it contains.
User
An individual that consumes an EPUB Publication using an EPUB Reading System.
EPUB Reading System (or Reading System)
A system that processes EPUB Publications for presentation to a User in a manner
conformant with this specification and its sibling specifications.
› 1.4 Conformance Statements
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD
NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described
in [RFC2119].
All sections of this specification are normative except where identified by the informative status label
"This section is informative". The application of informative status to sections and appendices applies to
all child content and subsections they may contain.
All examples in this specification are informative.
› 1.5 Namespace prefix mappings
For convenience, the following namespace prefix mappings [XMLNS] are used throughout this
specification:
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prefix namespace URI
epub http://www.idpf.org/2007/ops
m http://www.w3.org/1998/Math/MathML
pls http://www.w3.org/2005/01/pronunciation-lexicon
ssml http://www.w3.org/2001/10/synthesis
svg http://www.w3.org/2000/svg
› 2 EPUB Content Documents
› 2.1 XHTML Content Documents
This section defines a profile of [HTML5] for creating XHTML Content Documents. An instance of an XML
document that conforms to this profile is a Core Media Type and is referred to in this specification and its
sibling specifications as an XHTML Content Document.
Unless otherwise specified, this specification inherits all definitions of semantics, structure and
processing behaviors from the [HTML5] specification.
CAUTION
The EPUB 3 XHTML Content Document definition references features in the W3C [HTML5]
specification that are still works in progress and may change in incompatible ways. When utilizing
such features, authors should consider the inherent risks in terms of the potential impact on
interoperability and document longevity.
› 2.1.1 Content Conformance
An XHTML Content Document must meet all of the following criteria:
Document Properties
› It must meet the conformance constraints for XML documents defined in XML Conformance
[Publications30].
› It must use the XHTML syntax [HTML5].
› It must be valid to the XHTML Content Document schema as defined in XHTML Content
Document Schema.
› For all document constructs used that are defined by [HTML5], it must conform to the
conformance criteria defined for those constructs in that specification, unless explicitly overridden
in HTML5 Deviations and Constraints.
› It must conform to all content conformance constraints defined in HTML5 Extensions and
Enhancements.
File Properties
› The XHTML Content Document filename should use the file extension .xhtml.
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NOTE
All Publication Resources referenced from an XHTML Content Document must conform to the
constraints for Publication Resources defined in EPUB Publication — Content Conformance
[Publications30]
› 2.1.2 Reading S ystem Conformance
A conformant EPUB Reading System must meet all of the following criteria for processing XHTML
Content Documents:
› Unless explicitly defined by this specification or its sibling specifications as overridden, it must
process XHTML Content Documents using semantics defined by the [HTML5] specification and
honor any applicable User Agent conformance constraints expressed therein.
› It must meet all Reading System conformance criteria defined in HTML5 Extensions and
Enhancements.
› It must recognize and adapt behaviorally to the constraints defined in HTML5 Deviations and
Constraints.
› It must meet the Reading System conformance criteria defined in Scripted Content Documents
— Reading System Conformance.
› It must support visual rendering of XHTML Content Documents as defined in EPUB Style Sheets
— Reading System Conformance.
› It should recognize embedded ARIA markup and support exposure of any given ARIA roles,
states and properties to platform accessibility APIs [WAI-ARIA].
› 2.1.3 HTML5 Ex tensions and Enhancements
This section defines EPUB 3 XHTML Content Document extensions to the underlying [HTML5] document
model.
› 2.1.3.1 Semantic Inflection
› 2.1.3.1.1 Introduction
This section is informative
Semantic inflection is the process of attaching additional meaning about the specific purpose and/or
nature an element plays in an XHTML Content Document. In the context of EPUB Publications, the
epub:type attribute is typically used to express domain-specific semantics, with the inflection(s) it carries
complementing the underlying [HTML5] host vocabulary. The applied semantics always refine the
meaning of their containing elements, never override their nature (e.g., the attribute can be used to
indicate a section is a chapter in a work, but cannot be used to turn p elements into list items to avoid
proper list structures).
Semantic metadata is not intended for human consumption; it instead provides a controlled way for
Reading Systems and other User Agents to learn more about the structure and content of a document,
providing them the opportunity to enhance the reading experience for Users.
This specification defines a method for semantic inflection using the attribute axis: instead of adding new
XML elements to the XHTML Content Document vocabulary, the epub:type attribute can be appended to
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existing elements to inflect the desired semantics. A mechanism to identify external vocabularies that
provide controlled values for the attributes is also defined.
› 2.1.3.1.2 The epub:type Attribute
The epub:type attribute inflects semantics on the element on which it appears. Its value is one or more
space-separated terms stemming from external vocabularies associated with the document instance, as
defined in Vocabulary Association.
The inflected semantic must express a subclass of the semantic of the carrying element. In the case of
semantically neutral elements (such as [HTML5] div and span), 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). Reading Systems must ignore inflected semantics that conflict with the carrying element.
NOTE
The epub:type attribute is intended to be functionally equivalent to the W3C Role Attribute [Role],
but with restrictions as specified in Vocabulary Association.
Attribute Name
type
Namespace
http://www.idpf.org/2007/ops
Usage
May be specified on all elements.
Value
A space-separated list of property [Publications30] values, with restrictions as defined in
Vocabulary Association.
› 2.1.3.1.3 Vocabulary Association
This specification adopts the vocabulary association mechanisms defined in Vocabulary Association
Mechanisms [Publications30], with the following modifications:
Default Vocabulary
The default vocabulary for Content Documents is defined to be the EPUB 3 Structural Semantics
Vocabulary.
Reserved Vocabularies
This specification does not reserve any prefixes.
The prefix Attribute
The prefix attribute definition is unchanged, but the attribute is defined to be in the namespace
http://www.idpf.org/2007/ops when used in Content Documents.
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Examples
The following example shows the epub:type attribute used to inflect footnote and note reference semantics. The
properties used are defined in the default vocabulary.
…
… 1 …
…
…
The following example shows the epub:type attribute used to inflect glossary semantics on an HTML5 definition list.
The property used is defined in the default vocabulary.
…
-
…
…
The following example shows the epub:type attribute used to inflect source publication pagebreak semantics. The
property used is defined in the default vocabulary. (Note that the dc:source [Publications30] element provides a means
of identifying the source publication to which the given pagination information applies.)
…
… …
…
› 2.1.3.1.4 Processing Requirements
A Reading System must process the epub:type attribute as follows:
› It may associate specialized behaviors with none, some or all of the terms defined in the default
vocabulary.
› It may associate specialized behaviors with terms given in vocabularies other than the default.
› It must ignore terms that it does not recognize.
When Reading System behavior associated with a given epub:type value conflicts with behavior
associated with the carrying element, the behavior associated with the element must be given
precedence.
› 2.1.3.2 SSML Attributes
› 2.1.3.2.1 Overview
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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 host languages.
This specification recasts the SSML 1.1 phoneme element as two attributes — ssml:ph and ssml:alphabet
— and makes them available within EPUB XHTML Content Documents.
Reading Systems with Text-to-Speech (TTS) capabilities should support the SSML Attributes as defined
below.
NOTE
For more information on EPUB 3 features related to synthetic speech, refer to Text-to-speech
[EPUB3Overview].
› 2.1.3.2.2 The ssml:ph attribute
The ssml:ph attribute specifies a phonemic/phonetic pronunciation of the text represented by the element
to which the attribute is attached.
Attribute Name
ph
Namespace
http://www.w3.org/2001/10/synthesis
Usage
May be specified on all elements with which a phonetic equivalent can logically be
associated (e.g., elements that contain textual information).
Must not be specified 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 being used.
This attribute inherits all the semantics of the SSML 1.1 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).
NOTE
Reading Systems that support the SSML Attributes and PLS Documents must honor the defined
precedence rules for these two constructs.
› 2.1.3.2.3 The ssml:alphabet attribute
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The ssml:alphabet attribute specifies which phonemic/phonetic pronunciation alphabet is used in the
value of the ssml:ph attribute.
Attribute Name
alphabet
Namespace
http://www.w3.org/2001/10/synthesis
Usage
Global, may be specified 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 1.1 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.
Reading Systems that support the SSML Attributes feature of this specification should support the ipa
alphabet.
› 2.1.3.3 Content Switching
› 2.1.3.3.1 Introduction
This section is informative
The switch element provides a simple mechanism through which Authors can tailor the Publication
content displayed to Users, one that isn't dependent on the scripting capabilities of the Reading System.
Reading System developers may choose to support XML vocabularies and new HTML elements that are
not valid in XHTML Content Documents. The switch mechanism encourages this type of development and
experimentation, but at the same time provides Authors who wish to take advantage of it the security of
knowing that their content will still display on any compliant Reading System (i.e., it maintains the
baseline requirement that all XHTML Content Documents be valid if none of the specialized markup is
supported).
Content switching is not just about encouraging future development, however; it can also be used to
create Publications that maintain a level of compatibility with older Reading Systems unable to handle
the new features of EPUB 3. For example, instances of MathML, now a native type, could be added
using switch elements so that EPUB 2 Reading Systems could instead provide fallback images or text.
› 2.1.3.3.2 Definition
› 2.1.3.3.2.1 The epub:switch Element
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The switch element allows an XML fragment to be conditionally inserted into the content model of an
XHTML Content Document.
Element name
switch
Namespace
http://www.idpf.org/2007/ops
Usage
In Flow and Inline content. Repeatable.
Attributes
id [optional]
The ID [XML] of this element, which must be unique within the document scope.
Content Model
In this order: case [1 or more], default [exactly 1].
A Reading System must individually process each switch element in a document to determine whether it
can render any of the child case elements (as determined by the value of their required-namespace
attributes).
For each switch encountered, the Reading System should render the content of the first case it supports,
but is free to select from any of the available options. If the Reading System does not support the markup
contained in any of the child case elements, it must render the contents of the default element.
The [HTML5] object element should be used to embed custom (non-core) content types in XHTML
Content Documents. Custom markup should be wrapped in a switch element only when the content it
represents is an integral part of the do
...
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