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Open Publication Structure (OPS) 2.0 v0.9871.0

Recommended Specification July 11, 2007September 11, 2007

Copyright © 2007 by 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.

Table of Contents

1: Overview

1.1: Purpose and Scope
1.2: Definitions
1.3: Relationship to Other Specifications

1.3.1: Relationship to XML
1.3.2: Relationship to XML Namespaces
1.3.3: Relationship to NVDL
1.3.4: Relationship to XHTML and DTBook
1.3.5: Relationship to CSS 1.3.6: Relationship to Unicode 1.3.7: MIME Media Types 1.3.8: XML Style Sheet Processing Instruction

1.4: Conformance

1.4.1: OPS Content Document Conformance OPS Content Document XHTML Content Document Requirements DTBook Content Document Requirements Out-of-Line XML Island Content Document Requirements

1.4.2: Reading System Conformance
1.4.3: Compatibility with Future Versions
1.4.4: Compatibility of OPS Version 2.0

1.5: Extensibility
1.6: Accessibility
1.7: Future Directions

2.0: OPS Content Document Vocabularies

2.1: Introduction
2.2: XHTML Modules in the OPS Preferred Vocabulary

2.2.1: Required Modules

2.3: Certain Element and Attribute Semantic Differences From, and Restrictions Beyond, XHTML 1.1

2.3.1: General Comments on URI References

2.3.2: body Element

2.3.3: cite Attribute

2.3.4: img Element

2.3.5: link Element

2.3.6: object and param Elements

2.3.7: script and noscript Elements

2.3.8: type attribute of the style element

2.3.9: Value of align attribute

2.4: DTBook Preferred Vocabulary

2.4.1: Introduction

2.4.2: DTBook Usage Requirements Exceptions to Section 4 of the DAISY/NISO Standard

2.5: SVG

2.5.1: General Notes on SVG Usage

2.5.2: SVG’s Use as a Standalone Image File

2.5.3: Mixing SVG and XHTML Mark-up in the Same Document

2.6: XML Islands

2.6.1: Introduction to XML Islands Use Cases Display Guidelines

2.6.2: Out-of-Line XML Islands Document Requirements Fallback Requirements Linking Requirements Document-Level Links Fragment Links

2.6.3: Inline XML Islands The switch Element and Contained Elements switch Element case Element required-namespace Attribute required-modules attribute default Element Processing Inline XML Islands Displaying Inline XML Islands Advanced Display Semantics Styling of Islands Linking Considerations Linking to switch Elements Broken Links NCX Requirements

2.7: Rendering of Documents on Reading Systems

3.0: OPS Style Sheets

3.1: Selectors

3.2: Value Types

3.2.1: URI Values

3.2.2: Integers and Real Numbers

3.2.3: Length

3.2.4: Percentages

3.2.5: Color

3.2.6: Time

3.2.7: Frequency

3.2.8: Strings

3.3: Properties

3.4: Embedded Fonts

Appendix A: The NVDL Definition of OPS XHTML Content Documents

Appendix B: The OPS Schema

Appendix C: Contributors

Appendix D: Acknowledgements

Appendix E: Supporting Information & Errata 1.0: Overview 1.1: Purpose and Scope

In order for electronic-book technology to achieve widespread success in the marketplace, Reading Systems need to have convenient access to a large number and variety of titles. The Open Publication Structure (OPS) Specification describes a standard for representing the content of electronic publications. Specifically:

   * The specification is intended to give content providers (e.g. publishers, authors, and others who have content to be displayed) and publication tool providers, minimal and common guidelines that ensure fidelity, accuracy, accessibility, and adequate presentation of electronic content over various Reading Systems.
   * The specification seeks to reflect established content format standards.
   * The goal of this specification is to define a standard means of content description for use by purveyors of electronic books (publishers, agents, authors et al.) allowing such content to be provided to multiple Reading Systems and to insure maximum presentational equivalence across Reading Systems.

Another related specification, the Open Packaging Format (OPF) Specification, defines the mechanism by which the various components of an OPS publication are tied together and provides additional structure and semantics to the electronic publication. Specifically, OPF:

   * Describes and references all components of the electronic publication (e.g. markup files, images, navigation structures).
   * Provides publication-level metadata.
   * Specifies the linear reading-order of the publication.
   * Provides fallback information for when extensions to OPS are employed.
   * Provides a mechanism to specify a declarative table of contents (the NCX).

The OPF specification is separated from this OPS markup specification to modularize the described packaging methodology separate from the described content. This will help facilitate the use of the packaging technology by other standards bodies (e.g. DaisyDAISY) in non-OPS contexts.

A third specification, the OEBPS Container Format (OCF) Specification, defines the standard mechanism by which all components of an electronic publication may be packaged together into a single archive for transmission, delivery and archival purposes. 1.2: Definitions

Content Provider

A publisher, author, or other information provider who provides a publication to one or more Reading Systems in the form described in this specification.


A feature that is permitted, but not recommended, by this specification. Such features might be removed in future revisions. Conformant Reading Systems must support deprecated features.

Extended Module

A module of a modularized XML vocabulary (i.e. a set of named modules is defined in its specification) that is not required to be supported by its specification (e.g. the XHTML ruby or forms modules in the OPS context).

Inline XML Island

An Inline XML Island is an XML document fragment using a non-Preferred Vocabulary or using an Extended Module that exists within an XHTML Preferred Vocabulary document within an OPS Publication.


A declarative table of contents (the Navigation Center eXtended or NCX).


NVDL (Namespace-based Validation Dispatching Language) is a specification which allows for cross-schema validation of documents. This specification uses the NVDL language as a means of unambiguously defining how various schemas are handled within the context of OPS.


The OEBPS Container Format defines a mechanism by which all components of an OPS Publication may be combined into a single file-system entity.


The Open eBook Publication Structure. Previous versions of this specification (OPS) and its related specification, OPF, were unified into the single OEBPS specification. For this version, OEBPS was broken into OPS and OPF to aid modular adoption of the specifications. OEBPS 1.2 was the highest version of the previous unified specification.


The Open Packaging Format is the sister-standard to this standard. It defines the mechanism by which all components of a published work conforming to this standard along with metadata, reading order and navigational information are packaged into an OPS Publication.

OPF Package Document

An XML document that describes an OPS Publication and references all files used by the OPS Publication that are not part of the OPF Package Document itself. It identifies all other files in the publication and provides descriptive information about them. The OPF Package Document is defined by the OPF Specification.


The Open Publication Structure — this standard.

OPS Content Document

An XHTML, DTBook, or Out-Of-Line XML Island that conforms to this specification that may legally appear in an OPF Package Document spine element.

OPS Core Media Type

A MIME media type that all Reading Systems must support.

OPS Publication

A collection of OPS Content Documents, an OPF Package Document, and other files, typically in a variety of media types, including structured text and graphics, that constitute a cohesive unit for publication.

Out-of-Line XML Island

An Out-of-Line XML Island is an XML document, which exists within an OPS Publication, and is either not authored using a Preferred Vocabulary or is authored using a Preferred Vocabulary but uses Extended Modules. It is an entirely separate, complete, and valid XML document.

Preferred Vocabulary

XML consisting only of OPS-supported XHTML modules and/or DTBook markup.


A person who reads a publication.

Reading Device

The physical platform (hardware and software) on which publications are rendered.

Reading System

A combination of hardware and/or software that accepts OPS Publications (preferably packaged in an OCF Container) and makes them available to consumers of the content. Great variety is possible in the architecture of Reading Systems. A Reading System may be implemented entirely on one device, or it may be split among several computers. In particular, a Reading Device that is a component of a Reading System need not directly accept OPS Publications, but all Reading Systems must do so. Reading Systems may include additional processing functions, such as compression, indexing, encryption, rights management, and distribution.

XML Document

An XML document is a complete and valid XML document as defined by XML 1.1 standard. (

XML Document Fragment

Referred to as either a document fragment or as an XML Document Fragment, as defined in Document Object Model Level 1 ( but with the additional requirement that they be well-formed.

XML Island

An Inline XML Island or an Out-of-Line XML Island.

XML Namespaces

Referred to as XML namespaces, or just namespaces, these must conform to XML Namespaces (


The XML Pointer Framework is a W3C specification that defines a method of pointing into specific locations within an XML document, thus identifying document fragments, as defined in XML Pointer Framework ( 1.3: Relationship to Other Specifications

This specification combines subsets and applications of other specifications. Together, these facilitate the construction, organization, presentation, and unambiguous interchange of electronic documents:

  1. Extensible Markup Language (XML) 1.1 (Second Edition) specification (; and
  2. Namespaces in XML 1.0 (Second Edition) specification (; and
  3. Document Object Model (Core) Level 1 (; and
  4. XML Pointer Framework (; and
  5. XHTML™ 1.1 - Module-based XHTML - Second Edition specification (; and
  6. Specifications for the Digital Talking Book (DTB) (; and
  7. Scalable Vector Graphics (SVG) 1.1 Specification (; and
  8. Cascading Style Sheets, level 2 specification (; and
  9. Unicode Standard, Version 4.0. Reading, Mass.: Addison-Wesley, 2003, as updated from time to time by the publication of new versions. (See for the latest version and additional information on versions of the standard and of the Unicode Character Database).; and
 10. Particular MIME media types ( and; and
 11. Associating Style Sheets with XML Documents (; and
 12. Web Content Accessibility Guidelines 1.0 (; and
 13. RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. (; and
 14. Synchronized Multimedia Integration Language (SMIL 2.1) (; and
 15. The OPF specification (; and
 16. Namespace-based Validation Dispatching Language (NVDL) (

1.3.1: Relationship to XML

OPS is based on XML because of its generality and simplicity, and because XML documents are likely to adapt well to future technologies and uses. XML also provides well-defined rules for the syntax of documents, which decreases the cost to implementers and reduces incompatibility across systems. Further, XML is extensible: it is not tied to any particular type of document or set of element types, it supports internationalization, and it encourages document markup that can represent a document’s internal parts more directly, making them amenable to automated formatting and other types of computer processing.

   * Reading Systems must be XML processors as defined in XML 1.1. All OPS Content Documents must be valid XML documents according to their respective schemas.

1.3.2: Relationship to XML Namespaces

Reading Systems must process XML namespaces according to the XML Namespaces Recommendation at

Namespace prefixes distinguish identical names that are drawn from different XML vocabularies. An XML namespace declaration in an XML document associates a namespace prefix with a unique URI. The prefix can then be employed on element or attribute names in the document. Alternatively, a namespace declaration in an XML document may identify a URI as the default namespace, applicable to elements lacking a namespace prefix. The XML namespace prefix is separated from the suffix element or attribute name by a colon.



The root element of all OPS Content Documents must explicitly specify the namespace of the document. For the XHTML Preferred Vocabulary, this namespace is For the DaisyDAISY Talking Book Preferred Vocabulary, this namespace is If the OPS namespace is used in a document it must be explicitly declared If a namespace prefix is used, it is recommended that authors bind the ops prefix to that namespace and not use ops as the prefix for other namespaces.


html xmlns="" xmlns:ops="">

As OPS has additional functionality and validation requirements beyond the preferred document types and XML islands, there are other namespaces associated with OPS, which are used in specific contexts. 1.3.3: Relationship to NVDL

This specification uses the NVDL language (see as a means to unambiguously define the interaction between the various schemas used in this specification. NVDL allows for interaction and validation between various XML schema languages. See Appendix A for a normative NVDL definition of OPS.

This specification does not require the use of NVDL tools to validate OPS documents, although such tools are available and may be used for validation. 1.3.4: Relationship to XHTML and DTBook

This specification recognizes the importance of current software tools, legacy data, publication practices, and market conditions, and has therefore incorporated certain XHTML 1.1 Document Type Modules and DTBook as Preferred Vocabularies. This approach allows content providers to exploit current XHTML and DTBook content, tools, and expertise.

To minimize the implementation burden on Reading System implementers (who may be working with devices that have power and display constraints), the Preferred Vocabularies do not include all XHTML 1.1 elements and attributes. Further, the modules selected from the XHTML 1.1 specification were chosen to be consistent with current directions in XHTML.

Any construct deprecated in XHTML 1.1 is either deprecated or omitted from this specification; CSS-based equivalents are provided in most such cases. Style sheet constructs are also used for new presentational functionality beyond that provided in XHTML. 1.3.5: Relationship to CSS

This specification defines a style language based on CSS 2. (Note that the CSS 2.1 specification is currently still at "Working Draft" status.) The style sheet MIME type text/x-oeb1-css has been deprecated in favor of text/css.

The CSS-based style sheet constructs in this specification define required rendering functionality. To minimize the burden on Reading System developers and device manufacturers, not all CSS 2 properties are included. A few additional properties and values have been added to support page layout, headers, and footers. These, taken together, constitute the OPS CSS 2.0 required subset.

In a number of cases, this specification does not require Reading Systems to provide the full range of rendering that a standard CSS style sheet might request. For example, some Reading Systems will use monochrome displays. It would neither be acceptable to limit all Reading Systems to monochrome, nor to declare color use a non-standardized extension beyond OPS. In such cases, the CSS settings are allowed, and keep their meanings; but a conforming Reading System may gracefully degrade to a simpler rendering.

A conforming Reading System must render all OPS CSS 2.0 required subset properties. A Reading System may support CSS properties beyond the OPS CSS 2.0 required subset, however, any unsupported properties must be gracefully degraded per the CSS 2.0 specification.

This specification supports the style attribute (though deprecated), the style element, and externally linked style sheets. Reading Systems must perform XML-namespace handling while processing style sheets.

Style sheets can be associated with an OPS Content Document in several ways:

   * by style attributes on specific XHTML elements (deprecated); and
   * by style elements within the XHTML head element; and
   * by an external style sheet identified on link elements in the XHTML head element; and
   * by an external style sheet identified via the processing instruction xml-stylesheet (see Section 1.3.8).

The relative priority of the first three cases is as defined for XHTML 1.1 and CSS 2. Style sheets linked via a processing instruction are treated as if they had been linked via XHTML link elements preceding any actual XHTML link elements. As defined in the Conformance section, if no style sheet is defined or no applicable style is found for a given element, XHTML rendering is the default as defined elsewhere in this specification.

External style sheets linked via the XHTML link element or by the processing instruction xml-stylesheet, however, may use thisCSS or any other style language, such as XSL (see Reading Systems are not required to support any style sheet language beyond the CSS specified herein.

Reading Systems that implement only the OPS CSS 2.0 required subset may ignore any style sheets using other style languages. Reading Systems that support extended style sheet functionality may choose among any of the other external style sheets. It is strongly recommended that unique MIME media types be defined for any style sheet languages supported beyond the OPS CSS 2.0 required subset, and that style sheets in those languages be detected by examining the MIME media type.

Use of the CSS position property values to achieve absolute positioning (i.e. absolute and fixed) is strongly discouraged. 1.3.6: Relationship to Unicode

Publications may use the entire Unicode character set, using UTF-8 or UTF-16 encodings, as defined by Unicode (see The use of Unicode facilitates internationalization and multilingual documents. However, Reading Systems are not required to provide glyphs for all Unicode characters.

Reading Systems must parse all UTF-8 and UTF-16 characters properly (as required by XML). Reading Systems may decline to display some characters, but must be capable of signaling in some fashion that undisplayable characters are present. Reading Systems must not display Unicode characters merely as if they were 8-bit characters. For example, the biohazard symbol (0x2623) need not be supported by including the correct glyph, but must not be parsed or displayed as if its component bytes were the two characters "&#" (0x0026 0x0023).

To aid Reading Systems in implementing consistent searching and sorting behavior it is required that Unicode Normalization Form C (NFC) be used (See 1.3.7: MIME Media Types

This specification defines a list of OPS Core Media Types that all Reading Systems must support and publications may include. Publications may include resources of other media types, but each such resource must include an alternative resource of an OPS Core Media Type using methods defined in this specification or the OPF specification.

The OPS Core Media Types are: MIME Media Type Reference Description image/gif Used for raster graphics image/jpeg Used for raster graphics image/png RFC 2083 Used for raster graphics image/svg+xml Used for rastervector graphics application/xhtml+xml XHTML 1.1 Used for OPS Content Documents application/x-dtbook+xml Used for OPS Content Documents text/css CSS 2.0 Used for OPS CSS-subset style sheets application/xml Used for Out-Of-Line XML Islands text/x-oeb1-document OEBPS 1.2 specification Deprecated; Used for Basic or Extended OEBPS 1.0.1 and 1.2 Documents text/x-oeb1-css OEBPS 1.2 specification Deprecated; Used for OEBPS 1.0.1 and 1.2 CSS-subset style sheets application/x-dtbncx+xml DTBook specification The NCX 1.3.8: XML Style Sheet Processing Instruction

This specification includes support for the XML style sheet processing instruction xml-stylesheet, defined in the W3C Recommendation "Associating Style Sheets with XML Documents" ( This processing instruction is placed in the prolog of the XML document. It can appear multiple times as can link. 1.4: Conformance

The keywords "must", "must not", "required", "shall", "shall not", "should", "recommended", "may", and "optional" in this document must be interpreted as described in RFC 2119.

This section defines conformance for OPS Content Documents and Reading Systems. 1.4.1: OPS Content Document Conformance

This section defines conformance for OPS Content Documents. OPS Content Document

A document is considered an OPS Content Document if and only if:

  1. it uses a combination of the XHTML subset defined in this document and OPS-specific content extensions such as Inline XML Islands and Inline SVG; or
  2. it is a document with the MIME media type application/x-dtbook+xml which conforms to the DTB specification ( and must not use OPS-specific content extensions such as Inline XML Islands or Inline SVG; or
  3. it is an XML document of any other MIME media type and is thus an Out-Of-Line XML Island XHTML Content Document Requirements

A conformant XHTML Content Document must meet these conditions:

  1. it is a well-formed XML document (as defined by XML 1.1); and
  2. it is encoded in UTF-8 or UTF-16; and
  3. it is a valid XML document according to the NVDL schema interaction provided in Appendix A; and
  4. it has a MIME media type of either application/xhtml+xml or text/x-oeb1-document (deprecated); and
  5. all XHTML elements and attributes not contained in an Inline XML Island are drawn from the XHTML subset identified in this document. DTBook Content Document Requirements

A document is a DTBook Content Document if and only if:

  1. it is a well-formed XML document (as defined by XML 1.1); and
  2. it is encoded in UTF-8 or UTF-16; and
  3. it is a valid XML document, according to the DTBook DTD (; and
  4. it has a MIME media type of application/x-dtbook+xml. Out-of-Line XML Island Content Document Requirements

A document is an Out-of-line XML Island Content Document if and only if:

  1. it is a well-formed and valid XML document (as defined by XML 1.1according to its schema); and
  2. it is encoded in UTF-8 or UTF-16; and
  3. it has a MIME media type other than application/xhtml+xml, text/x-oeb1-document or application/x-dtbook+xml.

1.4.2: Reading System Conformance

This specification defines only one level of conformance for a Reading System. A Reading System is conformant if and only if it processes documents as follows:

When presented with an OPS Content Document the Reading System must:

  1. correctly process the XML as required in the XML 1.1 specification, including that specification’s requirements for the handling of well-formedness errors; and
  2. recognize all markup described as permitted in this specification and processes it consistently with the corresponding explanations in this specification and in those of XHTML 1.1, CSS 2, and DTBook (in case of any conflict, this specification takes precedence); and
  3. not render img or object elements of unsupported media types, in the absence of fallbacks. These fallbacks are clearly defined herein — img in Section 2.3.4 and object in Section 2.3.6; and
  4. verify the existence of the appropriate namespace specifications, as defined in the Relationship to XML Namespaces section above.

1.4.3: Compatibility with Future Versions

It is the intent of the contributors to this specification that subsequent generations of this specification continue in currently established directions. Specifically:

   * Content format standards will be compatible with W3C, IETF and other applicable standards; and
   * Future versions of this specification are expected to continue to improve alignment with XML-based specifications, requiring further XML processing capability of OPS-conformant Reading Systems, and enabling support for other applicable XML-related standards; and
   * Future versions of this specification are expected to improve the richness of hyperlinking in OPS documents; and
   * Any required functionality not present in relevant official standards shall be defined in a manner consistent with its eventual submission to an appropriate standards body as extensions to existing standards; and
   * Continued alignment with the affiliated OPF specification; and
   * Continued alignment and integration with the OCF content packaging standard.

1.4.4: Compatibility of OPS Version 2.0

Version 2.0 of OPS offers fairly significant enhancements over its preceding version, OEBPS 1.2. Version 2.0 adds substantial functional enhancements over 1.2, these include: supporting enhanced control over content presentational fidelity, providing an enhanced extension mechanism, improving accessibility, and improving alignment with the standards upon which OPS is based. Specifically, the following are the most substantive additions:

   * XML 1.1 is incorporated, and the bar has been raised from XML "well-formedness" to XML validity.
   * XML namespace processing is now required.
   * The concept of Basic and Extended documents has been removed and replaced with two XML Preferred Vocabularies and a new XML island-based extension mechanism.
   * The OPS subset of the XHTML element set has been replaced with reference to specific modules within XHTML 1.1.
   * The DTBook element set is now a Preferred Vocabulary.
   * Support for SVG has been added.
   * Support for embedded fonts has been added.
   * The OEBPS 1.2 Package has been extended for enhanced navigation and accessibility and the documentation thereof has been moved into the now separate OPF specification.
   * Older OEBPS-specific MIME types have been deprecated and replaced with more widely used standard MIME types.

While most changes from version OEBPS 1.2 to OPS 2.0 have been done via deprecation rather than removal of previous functionality, OEBPS version 1.2 is not a fully compatible subset of OPS 2.0 (e.g. new XML validity and namespace processing requirements). 1.5: Extensibility

XML Islands are the recommended mechanism for adding functionality, information or structure beyond that supported by the Preferred Vocabularies.

Out-Of-Line XML Islands may be used in any publication. Inline XML Islands maymust not only be used within documents authored using other than the XHTML Preferred Vocabulary. 1.6: Accessibility

This specification incorporates features that ensure content can be made accessible to, and usable by, persons with reading disabilities. Existing accessibility features developed by the World Wide Web Consortium (W3C) for XHTML 1.1 for content accessibility are incorporated into this specification.

OPS XHTML Content DocumentsPublications? should be authored in accordance with the W3C Web Content Accessibility Guidelines 1.0 ( or, if it is released while the Working Group is active, the Web Content Accessibility Guidelines 2.0 (the current draft is available at to ensure that the broadest possible set of users will have access to books delivered in OPS format.

In addition, recommendations from the W3C HTML 4.0 Guidelines for Mobile Access ( and the W3C Web Accessibility Initiative's proposed User Agent Guidelines ( ought to be reviewed and applied by OPS implementers to ensure that Reading Systems will be in conformance with accessibility requirements. 1.7: Future Directions

This specification is designed to take advantage of current practices while preparing for future developments. Although details of subsequent versions of this specification remain to be determined, it is the expectation of the Publication Structure Working Group that continued evolutionary development will occur. The themes driving the creation of version 2.0 of OPS are: standards compliance (e.g. full namespace support), accessibility support, support for any XML document typesupport for a wide-range of XML document vocabularies, enhanced navigation support, and improved content presentational fidelity.

Other themes deemed important for future versions include: more rigorous separation of content and presentation, greater accessibility, better support for international content, Reading Device-specific presentation control and/or Reading Device profiles, enhanced support for inter-Publication linking, layering and managing markups (e.g. inking, highlighting, notes) within Publications, application-specific markup (e.g. math, chemical), multiple reading orders, and support for active content (e.g. multimedia, scripting), all while maintaining alignment with relevant standards. Additionally, maintaining backward compatibility to this version of this specification ought to remain a high priority. Future directions can be tracked at 2.0: OPS Content Document Vocabularies 2.1: Introduction

OEBPS 1.2 and its predecessors specified a "Basic" document vocabulary, drawn from the XHTML 1.1 document type, which all Reading Systems were required to support. This specification no longer creates its own subset of XHTML 1.1, but instead references entire XHTML modules, as described in XHTML Modularization 1.1 ( In addition to XHTML, OPS adds the DAISY DTBook document type as a Preferred Vocabulary (see

The XHTML modules listed in this section and the DTBook vocabulary are considered the OPS Preferred Vocabularies. The concepts of "Basic" and "Extended" documents are no longer used by this specification. OPS publications should use one of the Preferred Vocabularies. Publications that use other vocabularies, either as entire documents or as XML fragments, must use the Inline or Out-Of-Line XML Island mechanisms, described elsewhere in this specification. XHTML modules beyond those listed here (Extended Modules) may be used in a conforming publication, but must follow the guidelines set forth in the XML Islands section of this document.

As with any DTD referenced from the DOCTYPE declaration, OPS XHTML Content Documents must not reference the XHTML DTD unless such documents are valid with respect to that DTD (i.e. it do not include Inline XML Islands or inline SVG). 2.2: XHTML Modules in the OPS Preferred Vocabulary 2.2.1: Required Modules

OPS requires all conforming Reading Systems to support the following modules consistent with their descriptions in the XHTML and HTML specifications, unless otherwise specified in this document. XHTML 1.1 Module Name Elements (non-normative) Structure body, head, html, title Text abbr, acronym, address, blockquote, br, cite, code, dfn, div, em, h1, h2, h3, h4, h5, h6, kbd, p, pre, q, samp, span, strong, var Hypertext a List dl, dt, dd, ol, ul, li Object object, param Presentation b, big, hr, i, small, sub, sup, tt Edit del, ins Bidirectional Text bdo Table caption, col, colgroup, table, tbody, td, tfoot, th, thead, tr Image img Client-Side Image Map area, map Meta-Information meta Style Sheet style Style Attribute (deprecated) style attribute Link link Base base 2.3: Certain Element and Attribute Semantic Differences From, and Restrictions Beyond, XHTML 1.1

As previously noted, the semantics and rendering behavior of the XHTML Preferred Vocabulary (elements, attributes, and associated attribute values) strictly follows that of XHTML 1.1. However, there are several restrictions beyond that of XHTML 1.1, as noted below. These restrictions have no effect on the XHTML 1.1 conformance of OPS documents. 2.3.1: General Comments on URI References

A number of attributes reference resources using URI values (Uniform Resource Identifier, see RFC 2396, Depending on the particular attribute, the URI referenced resource can either be an abstract entity or a physical object.

Except where noted or where not applicable, Reading Systems may use or render a URI referenced physical resource not listed in the Manifest (i.e., it is not a component of the Publication), but they are not required to do so. 2.3.2: body Element

It is assumed, in formatting, that the default rendering for body is consistent with the CSS property page-break-before having been set to right (which behaves like always on one-page Reading Systems), but may be overridden by an appropriate style sheet declaration. 2.3.3: cite Attribute

The optional attribute cite may be used in blockquote, q, del and ins to provide a URI citation for the element contents. Reading Systems are not required to process or use the referenced URI resource, whether or not the resource is listed in the Manifest. 2.3.4: img Element

The inline element img should only be used to refer to images with OPS Core Media Types of GIF (, PNG (RFC 2083), JPG/JFIF ( or SVG ( The required URI attribute, src, is used to reference the image resource, which must be listed in the Manifest.

The required alt attribute should contain a brief and informative textual description of the image. This text may be used by Reading Systems as an alternative to, or in addition to, displaying the image. The text is also an acceptable fallback for an img with src referencing a non-OPS Core Media Type for which no viable fallback was found in the manifest. The alt textual description is useful for Reading Systems having limited resolution displays, or for non-visual presentation. Use of the object element is the preferred mechanism for including non-core media types in an OPS Content Document.

For long descriptions, the optional title attribute may be used. Reading Systems may display the title attribute in addition to or in place of the alt text or displaying the image.

For greater accessibility, it is strongly recommended that OPS Content Document authors include a URI reference in the optional longdesc attribute referencing a resource (such as another OPS Content Document in the Publication) describing the image in finer detail. Reading System developers are also strongly urged to recognize and render in an appropriate fashion (and with accessibility in mind) the resource specified in longdesc. For further information on the use of this attribute and related accessibility attributes, see 2.3.5: link Element

The link element allows for the specification of various relationships with other documents. Reading Systems must recognize external style sheet references specified via the href attribute and the associated rel attribute (for the values rel="stylesheet" and rel="alternate stylesheet".) 2.3.6: object and param Elements

The object element is the preferred method for generic object inclusion. When adding objects whose data media type is not drawn from the OPS Core Media Type list or which reference an object implementation using the classid attribute, the object element must specify fallback information for the object, such as another object, an img element, or descriptive text. Inline fallback information is provided as OPS content appearing immediately after the final param element that refers to the parent object. Descriptive text for the object, using inline content, an included OPS Content Document, or some other method, should be provided to allow access for people who are not able to access non-textual content.

The classid attribute of an object gives the URI value of an implementation for the object. Conformant Reading Systems are not required to render objects that use external implementations, although they may do so. The MIME media type values for the codetype and type attributes must match those specified in the Publication's Manifest.

The associated param empty element is used to specify initialization values for objects. The param element must only appear before the renderable content of an object. Reading Systems must examine only param elements that are direct children of the object.


object classid="clsid:AFAFAFA-0101-1010-0101-ABABABABABA"

  <param name="code" value="TicTacToe.class">
  <param name="codebase" value="html/">
  <param name="type" value="application/x-somescriptinglanguage">
  <param name="model" value="models/TicTacToe.model">
  <param name="scriptable" value="true">
  <object type="image/png" data="tictactoe.png">
          Tic-Tac-Toe, a <em>dull</em> game.


2.3.7: script and noscript Elements

Reading Systems must not, by default, render the textual content of the script element, and should not execute the script itself. The content must be readable without execution of script elements.

If noscript is included, whose purpose is to display some message if the Reading System chooses not to execute the script, it must appear after the closing tag of the script it is associated with. Reading Systems must, by default, render the content contained in noscript if they do not execute script (as is recommended), the default of which can be overridden by CSS display:none. Note that for XHTML 1.1 conformance the content model for noscript is Block.mix (block level elements plus the "level-independent" elements); it cannot directly contain text or inline elements and is identical to the content model for body and blockquote, even if noscript itself appears inline.

The attribute type, which specifies the scripting language for script, is required.

One potential problem with script, whose content model is #PCDATA, is that if the code contains the characters "<" and "&", there is a potential conflict with XML. Thus, these characters, if used, must either be escaped, or put into a CDATA section. Reading System developers who include script execution capability need to be aware of this potential problem. 2.3.8: type attribute of the style element

The type attribute of the style element is required (per XHTML 1.1 requirements) and must be given the value of text/css or the deprecated text/x-oeb1-css. For browser rendering of an individual OPS Content Document as an XHTML 1.1 document, instances of the deprecated text/x-oeb1-css should be changed to text/css. 2.3.9: Value of align attribute

The value of char for the align attribute is not included in the OPS XHTML subset. To achieve similar formatting, use the CSS text-align property with a string value. 2.4: DTBook Preferred Vocabulary 2.4.1: Introduction

DTBook is an XML vocabulary defined in the DAISY/NISO standard, formally, the ANSI/NISO Z39.86-2005 Standard. This vocabulary is specifically designed for eBook content. Many structures not found in XHTML are included: footnotes, sidebars, annotations, page numbers, etc. Identifying the beginning of pages and the number of the page in the original print publication enables direct NCX navigation to the beginning of each page as reflected in the print publication. These pages will vary in size from the screens of information displayed by a typical Reading System. The retention of print page marking will enable a user to move to the identical location as someone who may be using a printed book.

It is strongly recommended that Content Providers select this XML Preferred Vocabulary for their educational publications and for content that is highly structured.

Many publishers may already have their content in DTBook as a result of the U.S. Individuals with Disabilities Education Improvement Act (IDEIA) of 2004 or other similar international legislation. Transforming it into an OPS publication can be accomplished with ease. Having the publication available using the DTBook vocabulary may help publishers market their publications to all students in the education market place, including those with print disabilities.

Section 4 of the DAISY/NISO Standard defines the DTBook DTD. This can be found on the NISO Web site at:

Additional information such as DTDs, issues tracking, samples and more can be found on the DAISY Web site at: 2.4.2: DTBook Usage Requirements

DTBook, as described in Section 4 of the DAISY/NISO Standard, must be followed in DTBook OPS Publications. The content must validate against the dtbook-2005-2.dtd, which was the latest version at the time of this writing. This DTD version, all previous versions, and all future versions will be available on the DaisyDAISY website. This will ensure that OPS Publications created under any version of the DTD remain valid.

It is essential that the semantics of the DTBook elements be applied correctly. To assist with this, a set of "Structure Guidelines" has been created. Documents created conforming to DTBook should use the Structure Guidelines for information regarding the correct application of the semantics of the elements. The Structure Guidelines can be found at: Exceptions to Section 4 of the DAISY/NISO Standard

There is a single attribute on elements in DTBook called smilref. This attribute is used for SMIL ( coordination. SMIL is not supported in OPS Publications. Leaving this attribute out of DTBook documents in OPS Publications must not will not cause validation errors. 2.5: SVG

Many images, such as maps, charts, graphs, etc., originate from vector graphics systems, not photographs. Such images can be represented in a vector (as opposed to raster) format that describes the image in terms of lines, curves and absolutely positioned blocks of text (as opposed to an array of pixels). Replacing raster images with vector ones makes documents more accessible and searchable. This additional effort on the part of Reading Systems and authors can improve accessibility significantly. Vector images also improve the visual quality of documents (since vector images are inherently scalable) and tend to decrease document sizes.

OPS Reading Systems must support SVG (Scalable Vector Graphics) as an OPS Core Media Type. 2.5.1: General Notes on SVG Usage

OPS supports the full SVG 1.1 Recommendation. The only exception is that since OPS is not targeting interactive content. SVG animation and scripting features are not supported and must not be used by publication authors; a Reading System should not render such content. CSS styling of SVG must be fully supported.

Text in SVG images should be selectable and searchable. SVG images may contain links (a elements) and thus may be used for navigation. If a Reading System supports "tabbing" through links, SVG links must be included.

Inline SVG is only supported within documents using the XHTML Preferred Vocabulary. It must not be used within DTBook documents. 2.5.2: SVG’s Use as a Standalone Image File

SVG content can be used in OPS in any place where other image types can be used. This includes:

   * References from XHTML img and object elements
   * References from DTBook img elements
   * References from SVG image elements
   * References from CSS properties that take an image URI as a parameter

To ensure maximum portability, the dimensions of SVG images should always be specified on the top-level SVG element . As with bitmap images, referencing elements may override an SVG image’s dimensions causing it to scale.

Each SVG image is considered a separate document for the purposes of styling. Referencing document style sheets do not apply to referenced SVG images, nor are CSS properties inherited by SVG images. Common styles should be achieved by creating style sheets that are referenced by both SVG and XHTML. Note that this is consistent with situations in which an object element references an XHTML element. 2.5.3: Mixing SVG and XHTML Mark-up in the Same Document

The other way of using SVG is to embed SVG mark-up directly in XHTML mark-up. The SVG root element (svg) must be considered replaced by its content in the CSS layout, so svg elements may be used anywhere XHTML img or object elements could be used. Other SVG elements may only be used as svg element descendants. Since SVG and XHTML elements have different namespaces, care needs to be taken to assign proper namespaces to each element using namespace prefixes or the xmlns attribute.

In this case, there is only one document and CSS style sheets apply to the document as a whole (including cascade and inheritance). In the usual manner, each element only makes use of the properties that are applicable to it. The root svg element’s role in CSS layout is determined by the display, float and position properties, just like it works for the img element. SVG image dimensions are determined by the width and height attributes on the root svg element (which are considered to be the replaced element’s intrinsic dimensions in the CSS box layout) and the width and height properties assigned by CSS. See for a definition of "replaced element" and "intrinsic dimensions." For portability, authors should avoid assigning XHTML-only CSS properties to SVG elements and vise-versa. 2.6: XML Islands

This section describes the markup and a processing model for the inclusion of generic XML content in OPS Publications. 2.6.1: Introduction to XML Islands

This section defines a method of including generic XML markup in OPS Publications. The motivation is to achieve the maximum backwards, sideways, and forwards compatibility with other XML vocabularies, including Extended OEBPS, as defined in OEBPS 1.2.

This is consistent with the stated future directions of OEBPS 1.2.

To that end, this document introduces the idea of "XML Islands." Two variants exist:

   * Out-Of-Line XML Islands
   * Inline XML Islands

Out-Of-Line XML Islands are any complete XML document that is not authored in one of the Preferred Vocabularies (i.e. DTBook or XHTML) or uses an Extended Module in an otherwise Preferred Vocabulary document.

An Inline XML Island is an XML document fragment using a non-Preferred Vocabulary or using an Extended Module of a Preferred Vocabulary that exists within an XHTML Preferred Vocabulary document within an OPS Publication. Inline XML Islands are also namespace-qualified to the OPS namespace and are not contained within object elements.

Inline XML Islands must not be used within documents using the DTBook Preferred Vocabulary; they must only be used within XHTML documents. Use Cases

Following are the use cases that justify the existence of XML Islands in OPS:

  1. Backwards Compatibility: There are an unknown number of documents that use Extended OEBPS 1.2 Documents which could be used in new Reading Systems. This document describes a method in which such documents could be used with minimal additions such as a few extra attributes in the OPS manifest, the addition of a single namespace declaration and/or the creation of a CSS style sheet.
  2. Sideways Compatibility: There are innumerable documents using non-Preferred XML vocabularies which exist and could be used in Reading Systems. This can be accomplished using the same methodology described above or using customized display semantics according to methods not available in a baseline OPS Reading System in conjunction with fallbacks to OPS Preferred Vocabularies.
  3. Forwards Compatibility: Experimentation with vocabularies that do not yet exist is enabled. Display Guidelines

OPS Reading Systems must follow these steps in handling the display of correctly marked up XML Islands:

  1. Semantic Styling: A Reading System may do more with XML Island content than provided for by the baseline requirements of OPS. This could include expanded rendering capabilities based on the Reading System’s intrinsic knowledge of the XML Island vocabulary (e.g. a TEI-reader, or a MathML reader).
  2. Fallback to OPS: A Reading System must use one of the fallback mechanisms if it lacks intrinsic knowledge of an XML Island’s vocabulary.

This allows the inclusion of non-Preferred Vocabulary content in a standardized way that lets a Reading System to do more than OPS requires as a baseline, while still allowing baseline Reading Systems to handle such content in a reasonable manner. 2.6.2: Out-of-Line XML Islands

An Out-Of-Line XML Island is a complete XML document that is not authored in one of the Preferred Vocabularies or uses an Extended Module in an otherwise Preferred Vocabulary document. Including an Out-Of-Line XML Island requires several declarations in various parts of the Publication. Document Requirements

An Out-Of-Line XML Island must be a valid XML document, as defined in XML 1.1 (according to its schema) and meet the other conformance requirements defined in section "Out-of-Line XML Island Content Document Requirements."

The following is a simple Out-Of-Line XML Island:

?xml version="1.0"?>

!DOCTYPE example SYSTEM "example.dtd">


  <title>This Is An Example</title>
  <paragraph>This is a paragraph with a <huge>big</huge> section
  of text that could be styled with OPS CSS!</paragraph>

/example> Fallback Requirements

The inclusion of an Out-Of-Line XML Island requires certain attributes and attribute values within a publication’s manifest to specify fallback information for Reading Systems that cannot natively process the Out-Of-Line XML Island’s vocabulary. See the OPF specification. Linking Requirements

Links that point into Out-Of-Line XML Islands must be resolved by a compliant OPS Reading System as follows: Document-Level Links

Links that point at an entire document in the publication must automatically resolve to the fallback document if the fallback document is used.

Link Source:

...<a href=”"chapter2.xml”">Chapter 2</a>...

Preferred Document - chapter2.xml:

               <title>Chapter 2</title>

Fallback Document - chapter2.html:


               <title>Chapter 2</title>


Manifest Fragment:

item href="chapter2.xml" id="chapter2"


item href="chapter2.html" id="chapter2fallback"


In this example, there are two possible behaviors. If the Reading System is capable of processing the document format of chapter2.xml then the link resolves to chapter2.xml. Otherwise, the link resolves to the fallback for chapter2.xml, which is chapter2.html. Fragment Links

Links that include document fragments must resolve to the fallback item, using the same fragment identifier. In the event that the fragment identifier does not exist in the fallback, the Reading System must place the link entry point at the start of the fallback document. 2.6.3: Inline XML Islands

An inline XML Island is an XML document fragment using a non-Preferred Vocabulary or using an Extended Module of a Preferred Vocabulary that exists within an XHTML Preferred Vocabulary document within an OPS Publication.

Processing Inline XML Islands is more complex than processing Out-Of-Line XML Islands, due to processing and display requirements. Out-Of-Line XML Islands are full XML documents, whose fallback options are defined in the OPF Package Document. Inline XML Islands are handled via a markup structure designed to simulate the common programming concept of a "switch" statement. The switch Element and Contained Elements

The switch element is a concept used in both SVG 1.1 and SMIL 2.1SMIL 2.x; however, OPS has requirements that are not identical to those specifications. As a result, the OPS implementation of the switch concept differs. Specifically, author intent is required in an explicit and clear fashion. In addition, the concept of a base fallback mechanism is provided. The normative definition of the switch element and its contained elements can be found in the OPS Schema.

The switch element and all contained elements reside in the OPS Namespace ( switch Element

The switch element is the containing element for an Inline XML Island. It contains zero or more case elements, and must contain one default element. The element names have been selected to be easily understood by those familiar with the "switch" feature of many programming languages.

An example of markup using the switch element follows:

ops:switch id="mathmlSwitch">

  <ops:case required-namespace="">
     <math xmlns="">
     <p>2x + y - z</p>

/ops:switch> case Element

The case element is used to contain non-Preferred Vocabulary or Extended Module markup. There are zero or more case elements in a switch element. The case element contains no content from the OPS namespace. This does not preclude it from containing content that is outside the OPS namespace, which is typically the case.

An OPS Reading System must not invalidate a document and must display nothing if a case element contains no content. required-namespace Attribute

The required-namespace attribute specifies the namespace of the XML vocabulary that the Reading System must support in order to process the content of the case element. A Reading System should process the content of the first case element that has a required-namespace attribute value that it supports. Note that processing of extra-OPS XML vocabularies is not required. Only the island’s fallback (default element) must be processed.

Documents that have a root element in the XHTML namespace must not use elements outside the XHTML namespace and, where allowed, the SVG namespace unless they are either specifically allowed there (e.g. SVG metadata element) or they are descendants of a case element that has a matching required-namespace attribute value. required-modules attribute

Some XML vocabularies are broken down into distinct modules, which may be supported in part or in whole by a compliant application. These vocabularies have a set of named modules defined in their specification, and some or all of these modules are optional – such optional modules are deemed Extended Modules in the specification.

A modularized XML vocabulary is considered supported by the Reading System if the Reading System supports the least number of modules required by the vocabulary's specification – supporting at least all non-Extended Modules of the XML vocabulary.

An Inline XML Island authored in a Preferred Vocabulary by definition incorporates use of Extended Modules. In this case, and with non-Preferred Vocabulary islands utilizing Extended Modules, the required-modules attribute must be present along with the required-namespace attribute. The attribute value for required-modules must be a comma-separated list containing the name(s) of the Extended Modules used in the Inline XML Island. The names of the modules are not case-sensitive, unless specifically defined otherwise in the XML vocabulary specification. Spaces in module names must be replaced with "-" for listing in the required-modules attribute value. For XHTML, in the context of OPS, the Extended Modules include ruby, forms, server-side-image-map, and intrinsic-events.

Note that listing the names of non-Extended Modules in a required-modules attribute value is also allowed; such modules are always considered to be supported if the XML vocabulary is supported. This can be useful both for clarity and in the case where there is a possibility that some modules may become optional in the later revisions of the specification (e.g. the currently deprecated Style Attribute XHTML module in OPS).

It is allowed, and sometimes useful, to provide a required-modules attribute on a case specifying a non-Preferred Vocabulary Inline XML island — either for clarity or to specify Extended Modules used in the non-Preferred Vocabulary.

An example of using required-modules to specify an XHTML module outside of OPS’s core supported modules follows:

ops:switch id="XHTMLServerSideSwitch?" xmlns:ops="">

       <ops:case required-namespace=""
               <a href="">
               <img src="example.gif" ismap="ismap"
                       title="Example Map"
                       alt="A picture of an example." />
               <img src="example.gif" usemap="map"
                       title="Example Map"
                       alt="A picture of an example." />
               <map name="map">
                       <area href="example1.html"
                               alt="Link to the first example."
                               shape="rect" coords="0,0,118,28" />
                       <area href="example2.html"
                               alt="Link to the second example"
                               shape="rect" coords="184,0,276,28" />

/ops:switch> default Element

The default element is nearly identical to the case element. The purpose of the default element is to provide compliant markup as a baseline (or fallback) for display of the switch. The default element must contain only XML nodes that would be allowed at the point of the document where its parent switch element was used. More precisely, a document is considered valid if and only if replacing all switch elements with the content of their child default elements yields a valid document. Processing Inline XML Islands

Inline XML Islands must be processed via the markup definitions found in the switch element and its contained elements. Displaying Inline XML Islands Advanced Display Semantics

Reading Systems must process case elements in the order they appear, and should render the content of the first supported case element recognized (i.e. the Reading System supports the vocabulary specified in the required-namespace). A Reading System must render only a single case or default element within a switch, ignoring the contents of all other case and default elements.

Reading Systems that do support the vocabularies of any of the case elements must render the contents of the default element. Styling of Islands

When styling is applied to a document that contains Inline XML Islands, style sheet cascading and inheritance rules are used for the complete document tree. However, OPS switch, case and default elements must ignore all styling properties that are assigned to them. In particular, those elements must not create any boxes (e.g. in terms of CSS box layout), as XHTML elements would. Linking Considerations

Deep linking into the content of Inline XML Islands cannot be accomplished consistently because various alternative Inline XML Islands must not contain elements with identical id attributes. It is therefore not possible to provide references that will resolve regardless of the case element selected for display. Linking to switch Elements

Reading Systems must recognize and display links that target switch elements even though the switch has no display characteristics of its own. Broken Links

Links into Inline XML Islands must be dropped without warning or error as they would be in a typical XHTML-compliant browser. NCX Requirements

Links from an NCX to Inline XML Islands must work identically to other links to Inline XML Islands. 2.7: Rendering of Documents on Reading Systems

A number of elements and attributes permit semantics that are not required of all Reading Systems. For example, some devices could be monochrome, or provide mainly audio or tactile interfaces. In such cases this specification generally requires Reading Systems to accept all syntax (such as attribute values) permitted for the Preferred Vocabulary, but does not require that they be honored. For example, a Reading System must parse and recognize the border attribute on table elements, but may choose to treat all values other than 0 the same as 1.

Note that this specification does not mandate specific rendering behavior for the OPS Preferred Vocabularies. Some Reading Systems could choose to express the intent of elements in presentation by closely following web browser usage — a blank line before a paragraph, but no first-line text-indent, for example. Other Reading Systems could gear their presentation towards sustained novel-like readability: for example, no extra whitespace between paragraphs, but text-indent on the first line of each. Still other systems, such as speech generators, could present particular elements or entire documents in completely different ways. 3.0: OPS Style Sheets

Like CSS style sheets, OPS style sheets are case-insensitive, except for the parts that are not under the control of CSS. In particular, OPS Content Documents are XML documents and, as such, their element names and attribute values are case-sensitive. Therefore, corresponding element names and attribute values in OPS style sheets are case-sensitive. Currently, this applies only to element names, attribute names and attribute values used in selectors.

Where there are differences in the syntax specified by CSS1 and CSS2, OPS style sheets follow the CSS2 syntax. A list of these differences can be found in section D3 of the W3C Recommendation REC-CSS2-19980512, "Cascading Style Sheets, level 2 (CSS2) Specification." OPS style sheets support the CSS construct of multiple declarations separated by semi-colons. Hence, the style sheet rules:

h1 { color: blue } h1 { font-weight: bold } h1 { font-size: 12pt }

are equivalent to:

h1 { color: blue;

    font-weight: bold;
    font-size: 12pt }

Multiple rules with identical declaration blocks can be combined into one rule by separating the selectors with commas. Thus the rules:

h1 {text-indent: 0em} h2 {text-indent: 0em} h3 {text-indent: 0em}

could be combined into the equivalent form:

h1, h2, h3 {text-indent: 0em}

OPS style sheets support all CSS white space characters. Specifically, the characters "space" (Unicode code 32), "tab" (9), "line feed" (10), "carriage return" (13), and "form feed" (12) can occur as whitespace. Comments of the syntax defined in the CSS2 specification may be used in OPS-conforming CSS style sheets.

This specification supports the inline style attribute (deprecated), the XHTML style element, and externally linked (via link elements or the xml-stylesheet processing instruction) style sheets. In DTBook, CSS style sheets can be included via the xml-stylesheet processing instruction. Thus, CSS styling can be applied to documents of both the XHTML and DTBook Preferred Vocabularies.

This specification assumes the use of selectors to be consistent with the definitions in the CSS2 Specification (see for details). For example, the rules for determining which of multiple rules are applied from a document’s style sheet are determined by the rules of inheritance, cascading and selector specificity (see for details).

If no style sheet is defined or no applicable style is found for a given XHTML OPS element, XHTML rendering is the default as defined elsewhere in this specification and the XHTML 1.1 specification.

This specification does not require that Reading Systems implement text-to-speech or other read-aloud technology. Reading Systems that do not implement such technology may ignore any CSS properties listed in this specification under the classification "aural style sheets," as well as the speak-header property listed under "Tables."

All properties apply to elements as defined in CSS. That is, most properties can apply to all elements, while a few are limited based on the value of the display property (for example, text-align only applies when the display type is block, not inline). Reading Systems are, however, not required to support every distinction; for example they may choose to map a specific length value for border-width to one of the named values for that property. 3.1: Selectors

Selectors specify the patterns that must be matched in the target document to determine the elements to which the style declaration(s) in the accompanying declaration block apply. If all conditions in the pattern are true for a certain element, the selector matches the element and the declarations in the declaration block are applied. This specification assumes a use of selectors that is consistent with the CSS2 Specification. Reading Systems must support all CSS2 selectors. 3.2: Value Types 3.2.1: URI Values

For those properties that take a URI value, the URI must point to a document of appropriate media type for the property in question. All such referenced documents must be contained within the OPF Package Document’s manifest. 3.2.2: Integers and Real Numbers

Real numbers are denoted by number, integer values by integer. Either could have an optional sign value (one of "+" or "-"), though particular properties could restrict the ranges and sign of numeric values. 3.2.3: Length

All non-zero coordinate and size values must have specified units. All units defined by CSS1 and CSS2 are supported: px Pixels ex x-height of current font em font-size of current font pt Points in Inches cm Centimeters mm Millimeters pc Picas 3.2.4: Percentages

Where percentage units are supported, they are used as defined for each property in the CSS specifications for which they are an allowed value. 3.2.5: Color

Current browsers support a host of keyword color names. XHTML 1.1 defines 16 named colors, as well as numeric values. OPS style sheets may use all CSS2 forms, however Reading Systems are not required to distinguish all these colors for rendering (otherwise monochrome devices would necessarily be non-conforming, which is not the intent). Black White Aqua Blue Fuschia Gray Green Lime Maroon Navy Olive Purple Red Silver Teal Yellow

#rrggbb six-digit hexadecimal

#rgb three-digit hexadecimal rgb(r, g, b) integers in the range 0-255 rgb(r%, g%, b%) floats in the range of 0.0% to 100.0% 3.2.6: Time

Units defined by CSS2 are supported: s Seconds ms Milliseconds 3.2.7: Frequency

Units defined by CSS2 are supported: Hz Hertz kHz Kilohertz 3.2.8: Strings

Strings must be quoted using either single or double quotes (Unicode codes 39 or 34, respectively). Nested strings must be escaped with a backslash (e.g. " a \"nested\" string"). To embed a line break in a string, use the escape "\A". The hexadecimal "A" is the line feed character in Unicode, but represents the generic notion of "newline" in CSS. 3.3: Properties

Default values for all supported CSS properties are as listed in CSS2.

The following table lists all CSS properties and values supported by this specification. Where not all values given in the CSS2 specification are listed for a given property, those values not listed are not supported by this specification. The column “Alternate display” indicates acceptable fallback display for CSS values that a Reading System cannot display as intended.

Properties that are unique to this specification have been underlined. CSS Structure Alternate Display CSS2 Section Media Types 7 @media 7.2.1 aural 7.3 all 7.3 Page Model 13.2 @page 13.2 :left 13.2.4 :right 13.2.4 :first 13.2.4 Box Model 8 Margins 8.3 margin-top, margin-bottom, margin-left, margin-right 8.3


percentage> margin [2] 8.3 auto 0 [1] Padding 8.4 padding-top, padding-bottom, padding-left, padding-right 8.4


percentage> padding [2] 8.4 Borders 8.5 border-top-width, border-bottom-width, border-left-width, border-right-width 8.5.1 thin medium thick

length> thin/medium/thick [3] border-width [2] thin/medium/thick [3] 8.5.1 border-top-color, border-bottom-color, border-left-color, border-right-color 8.5.2

color> [4] transparent border-color [2] 8.5.2 border-top-style, border-bottom-style, border-left-style, border-right-style 8.5.3 none hidden dotted solid dashed solid solid double solid groove solid ridge solid inset solid outset solid border-style [2] 8.5.3 border-top, border-bottom, border-left, border-right [2] 8.5.4 border [2] 8.5.4 Visual Display Model 9 display [5] 9.2.5 none inline block run-in table inline-table table-row-group table-header-group table-footer-group table-column-group table-row table-column table-cell table-caption inherit oeb-page-head [6] oeb-page-foot [6] float 9.5.1 left right none inherit clear 9.5.2 none left right both inherit direction 9.1 ltr rtl inherit unicode-bidi 9.1 normal embed bidi-override inherit oeb-column-number [13] auto

integer> 1 Visual Formatting Model Details 10 width 10.2


percentage> auto inherit min-width 10.4


percentage> inherit max-width 10.4


percentage> auto inherit height 10.5


percentage> auto inherit min-height 10.7


percentage> inherit max-height 10.7


percentage> none inherit line-height 10.8.1 normal



percentage> inherit vertical-align 10.8.1 baseline sub super top text-top [7] middle bottom ext-bottom [8] inherit Generated Content, Automatic Numbering, and Lists 12 content [9] 12.2

string> inherit list-style-type 12.6.2 none disc circle square decimal decimal-leading-zero lower-roman upper-roman lower-greek Decimal upper-greek Decimal lower-alpha lower-latin upper-alpha upper-latin hebrew Decimal armenian Decimal georgian Decimal cjk-ideographic Decimal hiragana Decimal katakana Decimal hiragana-iroha Decimal katakana-iroha Decimal inherit list-style-position 12.6.2 inside outside inherit list-style [2] 12.6.2 Paged Media 13 page-break-before 13.3.1 auto always avoid left [10] right [10] inherit page-break-after 13.3.1 auto always avoid left [10] right [10] inherit page-break-inside 13.3.1 auto avoid inherit orphans 13.3.3

integer> inherit widows 13.3.3

integer> inherit Colors and Backgrounds 14 color 14.1

color> [4] inherit background-color 14.2.1

color> [4] transparent inherit Fonts 15 font-family 15.2.2

family-name> sans-serif serif monospace inherit font-style 15.2.3 normal italic [11] oblique [11] inherit font-variant 15.2.3 normal small-caps font-weight 15.2.3 normal bold 100-900 [3] inherit font-size 15.2.4 xx-small x-small small medium large x-large xx-large smaller larger

length> [3]

percentage> [3] inherit font [2] 15.2.5 Text 16 text-indent 16.1


percentage> inherit text-align 16.2 left right center justify inherit text-decoration 16.3.1 none line-through underline inherit white-space 16.6 normal pre nowrap inherit Tables 17 caption-side 17.4.1 top bottom left right inherit table-layout 17.5.2 fixed auto inherit speak-header 17.7.1 once always inherit Aural Style Sheets 19 volume 19.2 silent x-soft soft medium loud x-loud

percentage> [3] 0–100 [3] inherit speak 19.3 normal none spell-out inherit pause-before 19.4


percentage> inherit pause-after 19.4


percentage> inherit pause [2] 19.4 cue-before 19.5

uri> none inherit cue-after 19.5

uri> none inherit cue [2] 19.5 speech-rate 19.8 x-slow slow medium fast x-fast faster slower

number> [12] inherit voice-family 19.8 male female child inherit pitch 19.8 x-low low medium high x-high

frequency> inherit stress 19.8 0-100 inherit richness 19.8 0-100 inherit speak-punctuation 19.9 code none inherit speak-numeral 19.9 digits continuous inherit

[1] Reading Systems may set the value of any margin property whose specified value is auto to 0.

[2] This is a shorthand property. The syntax for its value is given in the CSS2 specification. Where this specification limits values or indicates alternate representations for properties abbreviated by this property, the same limits and alternate representations apply to this property.

[3] Reading Systems may map to one of the keyword values listed for this property.

[4] See Section 3.2.5 on color units.

[5] CSS2 provides a full description of the various table values and their correct renderings. Please refer to the CSS2 Tables specification ( for a more detailed discussion of the various table values.

CSS2 and XHTML provide similar but subtly different algorithms for rendering table data. These algorithms tend to generate the same results, but there are a few exceptions. In such cases, conforming Reading Systems must produce output consistent with the algorithm specified by CSS2.

When using tables, authors should follow the Techniques for Web Accessibility Guidelines ( for maintaining as much semantic information as possible. That document describes good practices for choosing how and when to use table tags, and when to use CSS properties. Specifically, see "Guideline 5: Create tables that transform gracefully" (

[6] The content of an element assigned display: oeb-page-head should be presented only as a header, and the content of an element assigned display: oeb-page-foot should be presented only as a footer. Neither should be simply presented as if it were inline or block. Reading Systems, however, are free to present headers and footers either in special areas as usual for paper publications, or to make them available in another way. For example, a device with a small screen might instead pop them up on demand. For purposes of page layout, these display values are similar to block boxes with an absolute position (i.e. a position value of fixed or absolute). That is, they are removed from the normal flow and a new block box is created with its own flow. Margins, padding and other block characteristics are determined as if the element had position: fixed set.

An element assigned display: oeb-page-head or display: oeb-page-foot shall not be considered in effect while any preceding content remains presented. For example, when rendered to a screen with appropriate style settings, the myhead-classed div element below would become the page header as soon as nothing preceding the containing div is displayed:


  <div class="myhead" style="display: oeb-page-head">
     The OEB Publication Structure: Introduction


Such a header (or footer) remains in effect until another header (or footer) is in effect instead, or until no part of its parent element remains presented (such as when the div is no longer visible in the above example), whichever occurs first.

[7] Reading System may map to top.

[8] Reading System may map to bottom.

[9] Must not be used within a style sheet whose @media value is other than aural.

[10] One-page Reading Systems must treat left and right as always.

[11] Reading Systems need not distinguish italic and oblique from each other.

[12] Number specifies the speaking rate in words per minute.

[13] Specifies a number of columns in which to render content; may be applied to all block level elements. Reading Systems are free to support integer values other than 1, or may map them to 1. Reading Systems may support column balancing. A value of auto allows the Reading System to decide on the optimal number of columns in which to render content, considering available width, font sizes, or any other metrics it considers relevant for readability. 3.4: Embedded Fonts

To provide authors with control over the appearance of the text, OPS supports the CSS2 font-face at-rule (@font-face). See section 15.3.1 of the CSS2 Recommendation. The following font descriptors must be supported:

   * font-family
   * font-style
   * font-variant
   * font-weight
   * font-size
   * src

For portability, authors must not use any other descriptors. Font files must carry all information needed for rendering Unicode characters. Fonts must not provide mappings for Unicode characters that would change the semantics of the text (e.g. mapping the letter "A" to a biohazard symbol). Content creators must not assume that any particular font format is supported. Fonts could be included in multiple formats by using a list of files for the src descriptor; the first supported format should be used. At least one file in OpenType? format should always be included in the list. It is advisable for a Reading System to support the OpenType? font format, but this is not a conformance requirement; a reading system may support no embedded font formats at all. Content creators should use comma-separated lists for font-family properties to specify fallback font choices.

Content creators must always honor usage restrictions that are encoded in OpenType? fonts (and many other font formats). Fonts that are marked "no embedding" must not be included in OPS Publications.

Any font files included in an OPS Publication must be included in the OPF manifest with appropriate media type. Appendices Appendix A: The NVDL Definition of OPS XHTML Content Documents

This NVDL specification references three XML schemas:

  1. The XHTML DTD
  2. The SVG RelaxNG schema
  3. The OPS RelaxNG schema

The first two of these are referenced externally; the OPS schema is defined in Appendix B.

?xml version="1.0" encoding="UTF-8"?>

rules xmlns=""

      startMode="valid-ops" xmlns:html="">

!-- mode that allows any elements -->

mode name="anything">



!-- mode that only allows either valid SVG fragment -->

!-- or arbitrary XHTML fragment -->

mode name="blessed-xhtml">

  <namespace ns="">
     <validate schema=""
  <namespace ns="">


!-- mode that only allows arbitrary SVG fragment -->

mode name="blessed-svg">

  <namespace ns="">


!-- mode that allows any elements -->

!-- any XHTML fragments are attached in place of -->

!-- the OPS fragment that invoked this mode -->

mode name="xhtml-attach">

  <namespace ns="">


!-- mode that allows any elements -->

!-- any SVG fragments are attached in place of the OPS fragment -->

!-- that invoked this mode -->

mode name="svg-attach">

  <namespace ns="">


!-- mode that allows any valid XHTML with SVG islands included -->

!-- and OPS switch elements with valid default clause -->

mode name="valid-ops">

  <namespace ns="">
     <validate schema=""
               schemaType="application/xml-dtd" useMode="xhtml-content"/>


!-- mode that validates SVG and OPS islands inside XHTML -->

mode name="xhtml-content">

  <namespace ns="">
     <validate schema=""
  <namespace ns="">
  <namespace ns="">
     <!-- doing two independent thing here -->
     <!-- first, attach XHTML islands from default element into the XHTML -->
     <!-- tree so that they can be validated in the right context -->
     <unwrap useMode="xhtml-attach">
        <context path="case" useMode="anything"/>
     <!-- next, validate OPS itself (switch element), paying attention to -->
     <!-- what can go inside case and default elements -->
     <validate schema="ops20.rng">
        <context path="case" useMode="anything"/>
        <context path="default" useMode="blessed-xhtml"/>


!-- mode that validates OPS islands inside SVG -->

mode name="svg-content">

  <namespace ns="">
  <namespace ns="">
     <!-- doing two independent thing here -->
     <!-- first, attach SVG islands from default element into SVG tree, -->
     <!-- so that they can be validated in the right context -->
     <unwrap useMode="svg-attach">
        <context path="case" useMode="anything"/>
     <!-- next, validate OPS itself (switch element), paying attention -->
     <!-- to what can go inside case and default elements -->
     <validate schema="ops20.rng">
        <context path="case" useMode="anything"/>
        <context path="default" useMode="blessed-svg"/>



Appendix B: The OPS Schema

?xml version="1.0" encoding="UTF-8"?>

grammar ns="" xml:lang="en"



  <ref name="OPS.switch"/>


define name="OPS.switch">

  <element name="switch">
        <attribute name="id">
           <data type="ID"/>
        <element name="case">
              <attribute name="id">
                 <data type="ID"/>
           <attribute name="required-namespace">
              <attribute name="required-modules">
              <ref name="OPS.switch"/>
     <element name="default">
           <attribute name="id">
              <data type="ID"/>


           <ref name="OPS.switch"/>



Appendix C: Contributors

This specification has been developed through a cooperative effort, bringing together publishers, Reading System vendors, software developers, and experts in the relevant standards.

Version 2.0 of this specification was prepared by the International Digital Publishing Forum (IDPF) Open eBook Publication Structure (OEBPS) Working Group. Members of the working group at the time of publication of revision 2.0 were:

   * Angel Ancin, iRex Technologies
   * Rick Bowes, Thomson Learning
   * Peter Brantley, Digital Library Federation
   * Clint Brauer, SONY
   * Ken Brooks, Thomson Learning
   * Janice Carter, Benetech
   * Richard Cohn, Adobe Systems, Inc.
   * Garth Conboy, eBook Technologies, Inc. (Working Group co-Chair)
   * Neil De Young, Hachette Book Group
   * Linh Do, Random House
   * Brady Duga, eBook Technologies, Inc.
   * Geoff Freed, WGBH
   * Markus Gylling, DaisyDAISY Consortium
   * Jonathan Hevenstone, Publishing Dimensions (Working Group Vice Chair)
   * Rick Johnson, VitalSource Technologies
   * George Kerscher, DaisyDAISY Consortium
   * Steve Kotrch, Simon & Schuster
   * Bill McCoy, Adobe Systems, Inc.
   * Jon Noring, Digital Pulp Publishing
   * Siobhan Padgett, Hachette Book Group
   * Mina Park, Holtzbrinck Publishers
   * John Rivlin, eBook Technologies, Inc. (Working Group co-Chair)
   * Tyler Ruse, CodeMantra
   * Mike Smith, Harlequin
   * Peter Sorotokin, Adobe Systems, Inc.
   * Jennifer Sutton, Benetech
   * Ben Trafford, Invited Expert
   * Gary Varnell, Osoft
   * Eli Willner, Green Point Technology Services
   * Ric Wright, Adobe Systems, Inc.

The prior version of the OPS specification, on which this effort is based, was OEBPS 1.2. OEBPS 1.2 was developed by the Open eBook Forum Publication Structure Working Group. Active members that that working group during development of OEBPS 1.2 were:

   * Jeff Alexander, Franklin Electronic Publishers
   * Garth Conboy, Gemstar eBook Group Limited (Version 1.2 Co-Editor)
   * Eva Conkright, Random House
   * Brady Duga, Gemstar eBook Group Limited (Version 1.2 Co-Editor)
   * Jerry Dunietz, Microsoft Corporation (Working Group Vice Chair)
   * David Goldstein, Versaware Inc.
   * Gene Golovchinsky, FX Palo Alto Laboratory, Inc. (Development Sub-Group Co-Chair)
   * Donald Goyette, McGraw-Hill
   * Rebecca Guenther, Library of Congress
   * Markku Hakkinen, isSound Corporation
   * Barbara Hammond, Nokia
   * Benjamin Jung, deepX
   * George Kerscher, DaisyDAISY Consortium
   * Christopher R, Maden, crism consulting
   * Bob Mathews, Adobe
   * Michael Moodie, National Library Service for the Blind and Physically Handicapped, Library of Congress
   * Jon Noring, Windspun Inc. (Maintenance Sub-Group Chair)
   * David Pawson, Royal National Institute for the Blind
   * Chris Powell, University of Michigan Library
   * James Pritchett, Recording for the Blind and Dyslexic
   * Allen Renear, Brown University Scholarly Technology Group (Working Group Chair)
   * Dorothea Salo, OverDrive, Inc. (Working Group Scribe)
   * Ilan Sender, Microsoft Corporation
   * Sheela Sethuraman, CAST
   * Roger Sperberg, e-bks, LLC
   * Patrick Stickler, Nokia
   * Lisa Rupe, Questia Media Inc.
   * Mikhail Vaysbukh, Data Conversion Laboratory
   * Garret Wilson, GlobalMentor, Inc. (Development Sub-Group Co-Chair)
   * Harrison Yee, Apex

Appendix D: Acknowledgements

The working group wishes to specifically acknowledge the contributions of the following individuals. Peter Sorotokin for authoring the OPS and OPF RelaxNG schemas, creation of the NVDL definition of OPS, and general technical acumen. Ben Trafford for the concept and drafting of XML Islands, as well as overall technical participation, and the XML templates used to produce the specifications. George Kerscher for drafting the OPF NCX section, providing consistent accessibility direction and broad technical input. Brady Duga and Jon Noring for directional contributions, specification editing and providing continuity with the historic OEBPS 1.2 effort. Garth Conboy for working group leadership and motivation, specification drafting and technical contributions. Appendix E: Supporting Information & Errata

For additional information about all IDPF specifications including sample files, specification implementations and other information, please visit our public forums at If errors in the specifications are identified following publication, please post these errors to the forums. The responsible Working Group will review the errors and post pending corrections to the specifications if required or necessary. Corrections will be incorporated into subsequent versions of the specifications.

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Last-modified: 2009-03-30 (月) 14:20:30 (4232d)