Open eBook Publication Structure 1.0

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1 Overview

1.1 Purpose and Scope

The purpose of the Open eBook Publication Structure is to provide a specification for representing the content of electronic books. Specifically:

•	The specification is intended to give content providers (e.g., publishers, and others who have content to be displayed) and tool providers minimal and common guidelines which ensure fidelity, accuracy, accessibility, and presentation of electronic content over various electronic book platforms.
•	The specification seeks to reflect established content format standards.
•	The goal of this specification is to provide the purveyors of electronic-book content (publishers, agents, authors et al.) a format for use in providing content to multiple reading systems.

This specification is based on the premise that in order for electronic-book technology to achieve widespread success in the marketplace, reading systems must have convenient access to a large number and variety of titles.

1.2 About This Version

This specification has been developed through a cooperative effort, bringing together publishers, reading system vendors, software developers, and experts in the relevant standards. This "Open eBook Authoring Group" is composed of:

Facilitator:

Victor McCrary, National Institute of Standards and Technology,
U.S. Department of Commerce

Authors:

Jeff Alger, Microsoft Corporation

Garth Conboy, SoftBook Press

Horace Dediu, BCL Computers

Steve DeRose, Brown University Scholarly Technology Group

Kimmo Djupsjöbacka, Nokia

Brady Duga, SoftBook Press

Jerry Dunietz, Microsoft Corporation

David Goldstein, Versaware Inc.

Gene Golovchinsky, FX Palo Alto Laboratory, Inc

Markku Hakkinen, The Productivity Works

Gunter Hille, Project Gutenberg-DE

Kate Hughes, Microsoft Corporation

George Kerscher, DAISY Consortium

Steve Kotrch, Simon & Schuster

Brian Lambert, Glassbook Inc.

Jon Noring, Exemplary Technologies

Aleksey Novicov, Softbook Press

David Ornstein, NuvoMedia, Inc.

Dhiren Patel, NuvoMedia, Inc.

Steve Potash, OverDrive Systems

Allen Renear, Brown University Scholarly Technology Group

Mike Riley, R.R. Donnelley & Sons Company

Ben Trafford, Exemplary Technologies

John Voiklis, Red Figure, Inc.

Garret Wilson, GlobalMentor, Inc.

Other Contributing Organizations:
Adobe

EAST Co., Ltd

IBM

Librius

Vadem

1.3 Definitions

Basic OEB Document

An OEB document which restricts itself to the constructs defined in the specification.

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.

Deprecated

A feature that is permitted, but not recommended, by this specification. Such features may become obsolete in future revisions.

Extended OEB Document

An OEB document which uses constructs beyond those in this specification, but uses the extension mechanism defined herein.

OEB Core Media Type

A MIME media type that all reading systems must support.

OEB Document

An XML document which conforms to this specification.

OEB Package

A file that describes an OEB publication. It identifies all other files in the publication and provides descriptive and access information about them.

OEB Publication

A collection of OEB documents and other files, typically in a variety of media types, including structured text and graphics, that constitutes a cohesive unit for publication.

Reader

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 OEB publications, and directly or indirectly makes them available to readers. Great variety is possible in the architecture of reading systems. A reading sytem may be implemented entirely on one device, or it may be split among several computers. In particular, a reading device that is part of a larger reading system need not directly accept OEB publications, but all reading systems must do so. Reading systems may include additional processing functions beyond the scope of this specification, such as compression, indexing, encryption, rights management, and distribution.

1.4 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. the XML 1.0 markup meta-language (http://www.w3.org/TR/REC-xml);

2. the XML namespace specification (http://www.w3.org/TR/REC-xml-names);

3. the HTML 4.0 document content markup language (http://www.w3.org/TR/REC-html40), with consideration of the pending XHTML 1.0 specification (http://www.w3.org/TR/xhtml1/);

4. the CSS 1 stylesheet language (http://www.w3.org/TR/REC-CSS1), with a very few properties also from CSS 2 (http://www.w3.org/TR/REC-CSS2);

5. the Dublin Core metadata language (http://purl.org/dc/) and the USMARC relator code list (http://www.loc.gov/marc/relators/re9802r1.html);

6. the Unicode character set (http://www.unicode.org);

7. particular MIME media types (http://www.ietf.org/rfc/rfc1738.txt).

1.4.1 Relationship to XML

OEB is based on XML because of its generality and simplicity, and because this increases the likelihood that documents will survive longer. XML also provides well-defined rules for the syntax of documents, which decreases the cost to implementers and reduces incompatibility across systems. Further, XML enables extensibility because it is not tied to any particular 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 formatting and other types of computer processing.

OEB reading systems must be XML processors as defined in XML 1.0. All OEB documents must be well-formed XML documents, although they need not be valid XML documents. However, this specification ensures that for any basic OEB document, there is a syntax form that:

•	is a valid XML document,
•	conforms fully to the OEB document DTD,
•	is expected to conform to XHTML 1.0 when that specification is issued, and
•	is effectively previewable in typical version 4 HTML browsers.

The last point above does not claim full HTML 4.0 conformance for one primary reason: HTML 4.0 supports the XML empty element syntax in practice (i.e., it works in browsers) but not in formal HTML 4.0 specifications prior to XHTML 1.0.

XML well-formedness requires characteristics beyond what HTML browsers typically require, such as:

•	Elements must be bounded by both start- and end-tags;
•	Elements must nest properly, with no overlaps;
•	Attribute values must be quoted;
•	Attribute assignments must use the non-minimized form (unlike some "border" usages);
•	All "<" and "&" characters intended as content must be escaped as "<" and "&";
•	All element names and attribute names must be consistent in case (all OEB 1.0 names are, as expected for XHTML 1.0, lower-case);
•	All empty elements must use the XML empty element syntax (this specification also requires whitespace before the trailing slash, although such space is optional in XML; for example, "<br />").

Empty elements are those (such as the HTML br and hr elements) that permit no content. The XML and formal HTML syntaxes for these are incompatible, though the XML form with whitespace before the trailing slash is accepted by most HTML browsers (and is strictly conformant XML, as XML ignores whitespace within tags. For this reason, this specification requires this (conforming) variation of the XML form (for example, "<br />"); this is the most portable syntax and it contributes the most to document longevity, even though, strictly speaking, it is not valid in HTML.

Syntactic transformation from valid HTML to well-formed XML is trivial (though semantic transformations that also add brand-new structure and information value may not be). Transformation from invalid but moderately clean HTML is also usually an easy process and easily automated: several free tools already exist for this, such as "Tidy" (see http://www.w3.org/People/Raggett/tidy/). Transformation from extremely dirty HTML to XML, however, is of unpredictable complexity.

Not all well-formed XML 1.0 documents are conformant OEB documents. This is because this specification imposes further constraints in order to improve interoperability. These constraints are the "OEB Common Requirements," defined below.

This specification defines two XML DTDs – the package DTD and the basic OEB document DTD. The package forms the "root" of a complete publication, and reading systems should use it to find and organize publication components. The basic OEB document DTD formally defines the HTML subset described in this specification.

1.4.2 Relationship to XML Namespaces

This version of the specification does not demand that reading systems process XML namespace prefixes according to the XML Namespaces Recommendation at http://www.w3.org/TR/REC-xml-names.

Namespace prefixes are a method for prefixing element and attribute names to distinguish identical names that are drawn from different definition sets. A prefix is associated with a unique URI by an XML namespace declaration. Alternatively, a namespace declaration 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 by a colon.

This specification forbids the use of an oeb: namespace prefix within OEB documents . The use of the dc: prefix, however, is required for Dublin Core metadata element attributes in the OEB package. An element within the OEB document that contains a namespace prefix is treated as an extended element, with the colon acting as a normal XML name character. Reading systems must recognize the colon as a valid name character within an OEB document.

For upwards compatibility, the element metadata in an OEB package is required to have an attribute of xmlns:dc="http://purl.o rg/dc/elements/1.0/" and xmlns:oebpackage="http://openebook.org/namespaces/oeb-package/1.0/". In addition, the Dublin Core elements will be declared in the OEB package DTD with an explicit prefix of dc:.

1.4.3 Relationship to HTML

This specification recognizes the importance of current software tools, legacy data, publication practices, and market conditions, and so is based on HTML. This approach allows content providers to exploit current HTML 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 publication structure does not include all HTML elements and attributes. The elements and attributes were selected from the HTML 4.0 specification and were chosen to be consistent with current directions in HTML and XHTML development and the emergence of XML. See Appendix A for a complete table of the element types in HTML 3.2, HTML 4.0, and OEB documents.

Any HTML construct deprecated in HTML 4.0 is either omitted from this specification or is deprecated; CSS-based equivalents are provided in such cases. Stylesheet constructs are also used for new functionality beyond that provided in HTML 4.0..

To achieve predictable results and to support upwards compatibility with future versions of this specification, it is strongly recommended that basic OEB documents be valid XML documents with respect to the OEB document DTD.

1.4.4 Relationship to CSS

This specification defines a style language based on CSS 1 and CSS 2, with a media type of "text/x-oeb1-css". The OEB Authoring Group is aware that this definition of a media type goes against the recommendation of the CSS Working Group (see http://www.w3.org/TR/REC-CSS 1), but has chosen to do so due to practical considerations.

The CSS-based stylesheet constructs in this specification have been included to define baseline rendering functionality. To minimize the burden on reading system developers and device manufacturers, not all CSS 1 or CSS 2 properties are included. A few additional properties and values have been added for supporting page layout, headers, and footers.

In a number of cases, this specification does not require reading systems to provide the full range of rendering that a standard CSS stylesheet 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 OEB. In such cases, the CSS settings are allowed, and keep their meanings; but a conforming reading system may gracefully degrade to a simpler rendering.

This specification supports the inline style attribute, the style element, and externally linked stylesheets. This specification does not require that any handling of XML namespaces be performed by the reading system in the processing of stylesheets.

Stylesheets can be associated with an OEB document in several ways:

1. by style attributes on specific HTML elements;

2. by style elements within the HTML header;

3. by an external stylesheet identified on a link element in the HTML head; and/or

4. by an external stylesheet identified via a processing instruction as defined in the W3C proposed recommendation "Associating stylesheets with XML documents" (http://www.w3.org/TR/xml-stylesheet), or its final form if and when it is adopted.

The relative priority of the first three cases is as defined for HTML 4.0 and CSS 2. Stylesheets linked via a processing instruction are treated as if they had been linked via HTML link elements preceding any actual HTML link elements. As defined in the Conformance section, if no stylesheet is defined or no applicable style is found for a given element, HTML rendering is the default as defined elsewhere in this specification and the HTML4.0 specification.

Styles attached via the first two methods listed above may use only those CSS constructs defined as supported in Section 4 of this specification. External stylesheets linked via the HTML link element or by processing instructions, however, may use this or any other style language, such as XSL (see http://www.w3.org/TR/WD-xsl).

Only those CSS constructs defined as supported in Section 4 of this specification may be included in stylesheets of type "text/x-oeb1-css". Stylesheets of other MIME media types may be substituted for the text/x-oeb1-css stylesheets at the discretion of the reading system.

The HTML 4.0 specification groups externally linked stylesheets into sets by their titles (including a "persistent" set for which the title is the null string). This specification requires that at least one stylesheet in each such set must be of MIME media type "text/x-oeb1-css".

Reading systems that implement only the OEB CSS subset may ignore any stylesheets using other style languages. Reading systems that support extended stylesheet functionality may choose among any of the other external stylesheets. It is strongly recommended that unique MIME media types be defined for any novel stylesheet languages supported, and that stylesheets in those languages be detected by examining the MIME media type.

1.4.5 Relationship to Dublin Core

The Dublin Core is designed to minimize the burden of cataloging on authors and publishers, while providing enough data to be useful. This specification supports the entire current set of Dublin Core metadata elements, supplemented with a small set of additional attributes addressing areas where more specific information may be useful. For example, the role attribute added to the dc:Contributor element allows for much more detailed specification of contributors to a publication, including their roles expressed via relator codes.

Content providers must include a minimum set of a metadata elements, defined in section 2.2, and should incorporate additional metadata to enable readers to discover publications of interest.

1.4.6 Relationship to Unicode

Publications may use the entire Unicode character set, in UTF-8 or UTF-16 encodings, as defined by Internet RFC 2279 (see http://info.internet.isi.edu/in-notes/rfc/files/rfc2279.txt). The use of Unicode facilitates internationalization and multilingual documents. However, reading systems are not required to provide glyphs for all Unicode characters.

Reading systems are required to 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. They 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).

1.4.7 MIME Media Types

This specification defines a list of "core" MIME media types that all reading systems must support and publications may include. Publications may include resources of other media types, but for each such resource must include an alternative resource of a core MIME media type (using methods defined in this specification).

The core OEB MIME media types are:

Media Type	Reference	Description
image/jpeg	RFC 2046	Used for raster graphics
image/png	RFC 2083	Used for raster graphics
text/x-oeb1-document	this specification	Used for basic or extended OEB documents
text/x-oeb1-css	this specification	Used for OEB CSS-subset stylesheets

1.5 Conformance

This section defines conformance for OEB documents, publications, and reading systems.

1.5.1 Document and Publication Conformance

This specification defines two named levels of conformance for OEB documents–basic and extended, and one conformance level for OEB publications.

1.5.1.1 Common Requirements

A conformant OEB document (both basic and extended), or conformant OEB package file, must meet these necessary conditions, referred to in this specification as the "common requirements:"

(i)	it is a well-formed XML document (as defined in XML 1.0);
(ii)	it begins with a correct XML declaration (e.g. <?xml version=’1.0’?>);
(iii)	it is encoded in UTF-8 or UTF-16;
(iv)	for empty elements it uses only the XML empty element syntax with whitespace before the trailing slash;
(v)	it does not include an internal declaration subset; and
(vi)	any attribute with a value of NMTOKEN, ID, or IDREF must be a XML name.

1.5.1.2 Basic OEB Document

A document is a basic OEB document if and only if:

(i)	it meets the common requirements;
(ii)	its DOCTYPE declaration, if any, references the basic OEB document DTD;
(iii)	it uses only the element names, attribute names, and attribute values defined in this specification; all element and attribute names must be in lower case;
(iv)	it uses element names, attribute names, and attribute values in a manner broadly consistent with intentions of the relevant descriptions in this specification and those of HTML 4.0 and the Dublin Core, with this specification taking precedence in the event of conflicts;
(v)	if external stylesheets are used, then at least one stylesheet in each title set (as described in the HTML 4.0 specification), including any "persistent" set, must be of MIME media type "text/x-oeb1-css"; and
(vi)	all style parameters specified within the document itself belong to the OEB CSS subset.

1.5.1.3 Extended OEB Document

A document is an extended OEB document if and only if

(i)	it meets the OEB common requirements;
(ii)	it uses elements, attributes, or attribute values not defined in this specification, or its DOCTYPE declaration references a DTD other than the basic OEB document DTD;
(iii)	for any element not in this specification it must provide an applicable style rule using only the OEB CSS subset;
(vii)	if external stylesheets are used, then at least one stylesheet in each title set (as described in the HTML 4.0 specification), including any "persistent" set, must be of MIME media type "text/x-oeb1-css"; and
(viii)	all style parameters specified within the document itself belong to the OEB CSS subset.

1.5.1.4 Validity

OEB documents, basic or extended, may or may not be valid (as defined in XML 1.0) with respect to an associated DTD. However, all OEB documents must be well-formed XML 1.0 documents.

1.5.1.5 Publication Conformance

A collection of files is a conforming OEB publication if and only if

(i)	it includes a single OEB package file that obeys the OEB Common Requirements listed above, and is a valid XML document conforming to the OEB Package DTD;
(ii)	the OEB package file includes one and only one manifest entry corresponding to each other file in the publication;
(iii)	the manifest entry for each file in the publication specifies a MIME media type for the file (see http://www.ietf.org/rfc/rfc2046.txt);
(iv)	each file whose manifest entry identifies it as being in one of the core MIME media types, conforms as defined for those MIME media types;
(v)	the dc-metadata element contains at least one dc:Identifier and at least one dc:Title element;
(vi)	the unique-identifier attribute of the package element is a correct XML IDREF to a dc:Identifier element;
(vii)	any extended values specified for the dc:Contributor element’s role attribute begin with "oth."; and
(viii)	any extended values specified for the guide element’s type attribute begin with "other.".

1.5.2 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:

A) When presented with a basic OEB document the reading system

(i)	correctly processes XML as required in the XML specification, including that specifications requirements for the handling of well-formedness errors; and
(ii)	recognizes all markup described as permitted in this specification and processes it consistently with the corresponding explanation(s) in this specification and in those of HTML 4.0, CSS 2, and Dublin Core (in case of any conflict, this specification takes precedence).

B) When presented with an extended OEB document the reading system

(i)	performs as required in (A.i and A.ii);
(ii)	recognizes element instances not from this specification and renders them according to any applicable stylesheet rules, as described in section 1.4.4;
(iii)	must continue processing, displaying the element inline, as if "display: inline" applied, for any element not dealt with by (i) and (ii); and
(iv)	does not render objects of unsupported media types, in the absence of fallbacks. These fallbacks are clearly defined in sections 2.3.1, 3.6.2, 3.7.3, 3.30 and 3.36.

C) When presented with an OEB package the reading system

(i) must process all elements and attributes as described in chapter 2 of this specification.

D) When providing navigation via the OEB spine, the reading system

(i)	must not render content that does not have the media type text/x-oeb1-document; and

E) When presented with one or more style sheets via the HTML link mechanism or the XML-stylesheet processing instruction, described in http://www.w3.org/TR/xml-stylesheet, the reading system

(i) is able to process the document in accordance with the text/x-oeb1-css style sheets; and

(ii) if stylesheets of a MIME media type other than text/x-oeb1-css are provided, may choose to substitute those stylesheets for the text/x-oeb1-css stylesheets. Reading systems (although not necessarily reading devices) which support other stylesheet media types must provide a mechanism for requesting that those stylesheets be ignored in favor of the text/x-oeb1-css stylesheets.

Note: Reading systems are not required to support XML entity and attribute declarations (beyond parsing past them as XML requires), because such constructs are not permitted in conforming OEB documents.

1.5.3 Compatibility with Future Versions

It is the intent of the authors of this specification that subsequent generations of this specification continue in the directions established by the 1.0 release. Specifically:

•	Content format standards will be compatible with W3C (and IETF) standards;
•	Future versions of this specification are expected to improve alignment with XML-based specifications, relaxing the constraints (on OEB 1.0 documents) that are more restrictive than XML, requiring further XML processing capability of OEB 1.0 conformant reading systems, and perhaps supporting other XML-related standards such as Xlink;
•	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
•	Future versions of OEB will support a clearer separation of content and formatting, while being fully backwards-compatible with this specification.

1.6 Extensibility

Use of extended OEB documents is the recommended mechanism for adding information and structure beyond that provided by the HTML subset defined in this specification, for example, to associate further semantics with content. Arbitrary non-OEB elements may be added as long as such elements are provided with style definitions in accompanying stylesheets.

For example, the following document would be an extended OEB document excerpt:

<chapter>
<milestone n="257" />
<chapterhead>Chapter one</chapterhead>
<p>Now is the time… </p>
</chapter>

if associated with a style sheet that contains the following excerpt:

chapter {page-break-before: always}
milestone      { }
chapterhead     {
     font-weight: bold;
     font-family: sans-serif;
     text-align: center;
     display: block;
     margin-top: 4ex
}

1.7 Accessibility

This specification incorporates features that ensure content can be made accessible and usable by persons with disabilities. Existing accessibility features developed by the World Wide Web Consortium (W3C) for HTML 4.0 for content accessibility are incorporated into the OEB specification.

OEB publications should be authored in accordance with the W3C Web Content Accessibility Guidelines 1.0 (http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/) to ensure that the broadest possible set of users will have access to books delivered in this format.

In addition, recommendations from the W3C HTML 4.0 Guidelines for Mobile Access (http://www.w3.org/TR/NOTE-html40-mobile/) and the W3C Web Accessibility Initiative’s proposed User Agent Guidelines (http://www.w3.org/TR/WD-WAI-USERAGENT/) should be reviewed and applied by OEB implementers to ensure that reading systems will be in conformance with accessibility requirements.

1.8 Future Directions

This specification is designed to take advantage of current practices while preparing for future developments. Although the nature of subsequent versions of this specification remain to be determined, it is the expectation of the authors of this specification that these releases will continue in the same directions, including: increasing functionality, accessibility, internationalization, extensibility, and more rigorous separation of content and presentation, while maintaining alignment with relevant standards. Further, maintaining backward compatibility with this version of this specification is a high priority. Future directions can be tracked at http://www.openebook.org.

2 The OEB Package

A publication conforming to this specification must include exactly one OEB package file, which specifies the OEB documents, images, and other objects that make up the OEB publication and how they relate to each other.

It is recommended that all package files use extension ".opf", in order to make them readily identifiable within the group of files making up a publication. Package files are of MIME media type "text/xml". This specification does not define means for physically bundling files together to make one data transfer object (such as using zip or tar).

It is not required that the OEB package DTD be physically included in every publication. If included, it should be referenced from the manifest (as described below for other files).

The major parts of the OEB package file are:

•	PACKAGE IDENTITY – a unique identifier for the OEB publication as a whole.
•	METADATA – Publication metadata (title, author, publisher, etc.).
•	MANIFEST – A list of files (documents, images, style sheets, etc.) that make up the publication. The manifest also includes fallback declarations for files of types not supported by this specification.
•	SPINE – An arrangement of documents providing a linear reading order.
•	TOURS – A set of alternate reading sequences through the publication, such as selective views for various reading purposes, reader expertise levels, etc.
•	GUIDE – A set of references to fundamental structural features of the publication, such as table of contents, foreword, bibliography, etc.

An OEB package must be a valid XML document conforming to the OEB package DTD. An informal outline of the package is as follows:

<?xml version="1.0"?>
<!DOCTYPE package
PUBLIC "+//ISBN 0-9673008-1-9//DTD OEB 1.0 Package//EN"
"http://openebook.org/dtds/oeb-1.0/oebpkg1.dtd">
<package>
metadata
manifest
spine
guide
</package>

The following sections describe the parts of the OEB package.

2.1 Package Identity

The package element is the outermost element in a package file; all other elements are nested within it.

The package must specify a value for its unique-identifier attribute. The unique-identifier attribute’s value specifies which dc:Identifier element, described in section 2.2.10, provides the package’s preferred, or primary, identifier. The package file’s author is responsible for choosing a primary identifier that is unique to one and only one particular package (i.e., the set of files referenced from the package file’s manifest).

Notwithstanding the requirement for uniqueness, reading systems must not fail catastrophically should they encounter two distinct packages with the same purportedly unique primary identifier.

2.2 Publication Metadata

The required metadata element is used to provide information about the publication as a whole. It contains a Dublin Core metadata record within a dc-metadata element, and supplemental metadata in an x-metadata element.

The dc-metadata element contains specific publication-level metadata as defined by the Dublin Core initiative (http://purl.org/dc/). The descriptions below are included for convenience, and the Dublin Core’s own definitions take precedence (see http://www.ietf.org/rfc/rfc2413.txt).

The x-metadata element must contain one or more instances of a meta element, analogous to the HTML 4.0 meta element, but applicable to the publication as a whole. The x-metadata element allows content providers to express arbitrary metadata beyond the data described by the Dublin Core language. Individual OEB documents may include the meta element directly (as in HTML 4.0) for document-specific metadata. This specification uses the OEB package file alone as the basis for expressing publication-level Dublin Core metadata.

For example:

The XML namespace mechanism (see http://www .w3.org/TR/REC-xml-names/) is used to identify the elements used for Dublin Core metadata without conflict. Note that there is no requirement on reading systems to process namespaces. This syntax is used to provide for upwards-compatibility.

The dc-metadata element can contain any number of instances of any Dublin Core elements. Dublin Core element names begin with the "dc:" prefix followed by a leading uppercase letter. Dublin Core metadata elements may occur in any order; in fact, multiple instances of the same element type (multiple dc:Creator elements, for example) can be interspersed with other metadata elements without change of meaning.

For upwards-compatibility, the element metadata in an OEB package is required to have an attribute of xmlns:dc="http://purl.org/dc/elements/1.0/" and xmlns:oebpackage="http://openebook.org/namespaces/oeb-package/1.0/".

Each Dublin Core field is represented by an element whose content is the field’s value. The dc:Title and at least one dc:Identifier must be included in the dc-metadata element. Dublin Core elements, like any other elements in the OEB package file, may have an id attribute specified. At least one dc:Identifier, that which is referenced from the package unique-identifier attribute, must have an id specified.

Because the Dublin Core metadata fields for Creator and Contributor do not distinguish roles of specific contributors (such as author, editor, and illustrator), this specification adds an optional role attribute for this purpose. See section 2.2.6 for a discussion of role.

This specification also adds a scheme attribute to the dc:Identifier element to provide a structural mechanism to separate an identifier value from the system or authority that generated or defined that identifier-value. See section 2.2.10 for a discussion of scheme.

This specification also adds a event attribute to the dc:Date element to enable content providers to distinguish various publication specific dates (for example, creation, publication, modification). See section 2.2.7 for a discussion of event.

For example:

<package unique-identifier="xyz">
<metadata>
          <dc-metadata xmlns:dc="http://purl.org/dc/elements/1.0/" xmlns:oebpackage="http://openebook.org/namespaces/oeb-package/1.0/">
          <dc:Title>Alice in Wonderland</dc:Title>
               <dc:Type>Novel</dc:Type>
               <dc:Identifier id="xyz"
               scheme="ISBN">123456789X</dc:Identifier>
               <dc:Creator role="aut">Lewis Caroll</dc:Creator>
          </dc-metadata>
     </metadata>
     ...
</package>

Attributes of elements within the dc-metadata element are not defined by the Dublin Core – only the elements’ contents are so defined.

The following subsections describe the individual Dublin Core metadata elements.

2.2.1 <dc:Title> </dc:Title>

The title of the publication. Although an OEB package must include at least one instance of this element type, multiple instances are permitted. Any reading system that displays title metadata to the user should either use the first dc:Title only, or all dc:Title elements.

2.2.2 <dc:Creator> </dc:Creator>

A primary creator or author of the publication. Additional contributors whose contributions are secondary to those listed in dc:Creator elements should be named in dc:Contributor elements.

Publication with multiple co-authors should provide multiple dc:Creator elements, each containing one author. The order of dc:Creator elements is presumed to define the order in which the creators’ names should be presented by the reading system.

This specification recommends that the content of the dc:Creator elements hold the text for a single name as it would be presented to the user.

The dc:Creator elements has two optional attributes, role and file-as. The set of values for role are identical to those defined in section 2.2.6 for the dc:Contributor element. The file-as attribute should be used to specify a normalized form of the contents, suitable for machine processing. For example, one might find

<dc:Creator file-as="King, Martin Luther Jr." role="aut">
Rev. Dr. Martin Luther King Jr.
</dc:Creator>

If a reading system displays creator information, the reading systems must display the contents of all dc:Creator elements, in the order provided, with appropriate separating spacing and/or punctuation.

2.2.3 <dc:Subject> </dc:Subject>

Multiple instances of the dc:Subject element are supported, each including an arbitrary phrase or keyword. This specification makes no attempt to standardize subject naming schemes, such as the Library of Congress Subject Heading System.

2.2.4 <dc:Description> </dc:Description>

Plain text describing the publication’s content.

2.2.5 <dc:Publisher> </dc:Publisher>

The publisher as defined in RFC2413.

2.2.6 <dc:Contributor> </dc:Contributor>

A party whose contribution to the publication is secondary to those named in dc:Creator elements.

Other than significance of contribution, the semantic of this element are identical to those of dc:Creator. Reading systems are free to choose to display dc:Creator information without accompanying dc:Contributor information.

The dc:Contributor element has two optional attributes, role and file-as. The file-as attribute is defined as for dc:Creator, and is documented in section 2.2.2.

The normative list of values used for the role attribute is defined by the USMARC relator code list (http://www.loc.gov/marc/relators/re9802r1.html). When roles are specified, the 3-character USMARC values must be used when applicable. Although that list is extensive, other values may be added if a required role is not covered by those predefined values. Such values must begin with "oth.", and shall be considered subdivisions of the "other" relator code. Like other constructs in this specification, these values are case-sensitive and must be coded entirely in lower-case.

For convenience, some relator code values are listed here as examples. Consult the USMARC code list cited above for the complete list.

Adapter [adp] Use for a person who 1) reworks a musical composition, usually for a different medium, or 2) rewrites novels or stories for motion pictures or other audiovisual medium.

Annotator [ann] Use for a person who writes manuscript annotations on a printed item.

Arranger [arr] Use for a person who transcribes a musical composition, usually for a different medium from that of the original; in an arrangement the musical substance remains essentially unchanged.

Artist [art] Use for a person (e.g., a painter) who conceives, and perhaps also implements, an original graphic design or work of art, if specific codes (e.g., [egr], [etr]) are not desired. For book illustrators, prefer Illustrator [ill].

Associated name [asn] Use as a general relator for a name associated with or found in an item or collection, or which cannot be determined to be that of a Former owner [fmo] or other designated relator indicative of provenance.

Author [aut] Use for a person or corporate body chiefly responsible for the intellectual or artistic content of a work. This term may also be used when more than one person or body bears such responsibility.

Author in quotations or text extracts [aqt]
Use for a person whose work is largely quoted or extracted in a works to which he or she did not contribute directly. Such quotations are found particularly in exhibition catalogs, collections of photographs, etc.

Author of afterword, colophon, etc. [aft]
Use for a person or corporate body responsible for an afterword, postface, colophon, etc. but who is not the chief author of a work.

Author of introduction, etc. [aui]
Use for a person or corporate body responsible for an introduction, preface, foreword, afterword, or other critical matter, but who is not the chief author.

Note: The author of a specific part of the book may be expressed using a meta element in that part.

Bibliographic antecedent [ant]
Use for the author responsible for a work upon which the work represented by the catalog record is based. This may be appropriate for adaptations, sequels, continuations, indexes, etc.

Book producer [bkp] Use for the person or firm responsible for the production of books and other print media, if specific codes (e.g., [bkd], [egr], [tyd], [prt]) are not desired.

Collaborator [clb] Use for a person or corporate body that takes a limited part in the elaboration of a work of another author or that brings complements (e.g., appendices, notes) to the work of another author.

Commentator [cmm] Use for a person who provides interpretation, analysis, or a discussion of the subject matter on a recording, motion picture, or other audiovisual medium.

Compiler [com] Use for a person who produces a work or publication by selecting and putting together material from the works of various persons or bodies.

Designer [dsr] Use for a person or organization responsible for design if specific codes (e.g., [bkd], [tyd]) are not desired.

Editor [edt] Use for a person who prepares for publication a work not primarily his/her own, such as by elucidating text, adding introductory or other critical matter, or technically directing an editorial staff.

Illustrator [ill] Use for the person who conceives, and perhaps also implements, a design or illustration, usually to accompany a written text.

Lyricist [lyr] Use for the writer of the text of a song.

Metadata contact [mdc] Use for the person or organization primarily responsible for compiling and maintaining the original description of a metadata set (e.g., geospatial metadata set).

Musician [mus] Use for the person who performs music or contributes to the musical content of a work when it is not possible or desirable to identify the function more precisely.

Narrator [nrt] Use for the speaker who relates the particulars of an act, occurrence, or course of events.

Other [oth] Use for relator codes from other formats which have no equivalent in USMARC or for terms which have not been assigned a code.

Photographer [pht] Use for the person or organization responsible for taking photographs, whether they are used in their original form or as reproductions.

Printer [prt] Use for the person or organization who prints texts, whether from type or plates.

Redactor [red] Use for a person who writes or develops the framework for an item without being intellectually responsible for its content.

Reviewer [rev] Use for a person or corporate body responsible for the review of book, motion picture, performance, etc.

Sponsor [spn] Use for the person or agency that issued a contract, or under whose auspices a work has been written, printed, published, etc.

Thesis advisor [ths] Use for the person under whose supervision a degree candidate develops and presents a thesis, memoir, or text of a dissertation.

Transcriber [trc] Use for a person who prepares a handwritten or typewritten copy from original material, including from dictated or orally recorded material.

Translator [trl] Use for a person who renders a text from one language into another, or from an older form of a language into the modern form.

2.2.7 <dc:Date> </dc:Date>

Date of publication, in the format defined by "Date and Time Formats" at http://www.w3.org/TR/NOTE-datetime and by ISO 8601 on which it is based. In particular, dates without times are represented in the form YYYY[-MM[-DD]]: a mandatory 4-digit year, an optional 2-digit month, and if the month is given, an optional 2-digit day of month.

The dc:Date element has one optional attribute, event. The set of values for event are not defined by this specification; possible values may include: creation, publication, modification.

2.2.8 <dc:Type> </dc:Type>

Dublin Core provides examples of resource types "such as home page, novel, poem, working paper, technical report, essay, dictionary." The Dublin Core is currently considering revisions to the usage of this field, and should be consulted for updated definitions.

2.2.9 <dc:Format> </dc:Format>

An enumerated list of formats for this content is being developed by the Dublin Core.

2.2.10 <dc:Identifier> </dc:Identifier>

A string or number used to uniquely identify the resource.

At least one dc:Identifier must have an id specified, so it can be referenced from the package unique-identifier attribute of Section 2.1.

The dc:Identifier element has an optional attribute, scheme. The scheme attribute names the system or authority that generated or assigned the text contained within the dc:Identifier element, for example "ISBN" or "DOI." The values of the scheme attribute are case sensitive.

This specification does not standardize or endorse any particular publication identifier scheme. Specific use of URLs or ISBNs is not yet addressed by this specification. Identifier schemes are not currently defined by Dublin Core.

2.2.11 <dc:Source> </dc:Source>

Information regarding a prior resource from which the publication was derived (see RFC 2413).

2.2.12 <dc:Language> </dc:Language>

If specified, the content must be an RFC 1766-compliant specification of the primary language of the content. (See http://www.ietf.or g/rfc/rfc1766.txt.) US English (en-us) is the default. The Dublin Core permits other descriptions as well; this specification does not.

2.2.13 <dc:Relation> </dc:Relation>

An identifier of an auxiliary resource and its relationship to the publication. An enumerated list of relationship types is currently under development by the Dublin Core.

2.2.14 <dc:Coverage> </dc:Coverage>

The place or time which the publication’s content addresses.

2.2.15 <dc:Rights> </dc:Rights>

A statement about rights, or a link to one. In this specification, the copyright notice and any further rights description should appear directly.

This specification does not address the manner in which a Content Provider specifies to a secure distributor any licensing terms under which readership rights or copies of the content may be sold.

2.3 Manifest

The manifest provides a list of all the files that are parts of the publication. The manifest element must contain one or more item elements. Each item describes a document, an image file, a stylesheet, or other component that is considered part of the publication.

Each item element contained within a manifest element must have an id attribute. In addition, each item element in the manifest must have an href attribute, which is a URI (if relative, the URI is interpreted as relative to the package file itself). Additionally, each item element must have its MIME media type specified via the media-type attribute.

The order of item elements in the manifest is not significant.

For example,

The URIs in href attributes of item elements in the manifest, may not use fragment identifiers.

2.3.1 Fallback items

This specification defines a set of core MIME media types that all conforming reading systems must support. For a publication that uses only those media types, the manifest merely needs to list the publication’s component files directly. However, content providers may construct publications that reference items of additional media types. In order that such publications can nevertheless be read by all conforming reading systems, content providers must always provide alternative "fallback" items for each such item. For every item that is not in a core media type, at least one of its associated fallback items must be of a type drawn from the set of core media types.

This specification defines two different mechanisms for specifying core media type fallbacks. For inline "replaced" elements, this specification relies on the HTML-based object element, described in section 3. For non-inline destinations, whether referenced from a document or a package, the fallback attribute of an item is used.

An item identifies a fallback item using its fallback attribute, which must specify the ID of the item element that identifies the fallback. Items referenced from fallback attributes may each specify a fallback attribute in turn, forming a longer "fallback path." For example,

If a fallback attribute points to an item that also has a fallback attribute, a reading system must continue down the fallback path until it reaches a reference to an item of a media type it can display. A reading system may continue further, and may display any item from the chain. Every item in a publication that is not of one of the core MIME media types must, directly or indirectly, specify a fallback path to an item of one of the core MIME media types.

Fallback paths must terminate; circular references are not permitted. Nevertheless, reading systems should not fail catastrophically if they encounter such a cycle.

2.4 Spine

Following the manifest, there must be one spine element, which defines a primary linear reading order of the publication. It specifies an ordered list of one or more OEB documents drawn from the manifest, using itemref elements contained within the spine element.

A publication must specify exactly one spine. Reading systems must treat the file named in the first itemref element within the spine as the first file to be rendered in the reading of the book. The successive files named in its itemref elements are those that are to be rendered using "next-page"-type functionality that may be available in the reading system.

The spine may refer only to item elements of media type text/x-oeb1-document. Content of other media types may be referenced via OEB documents, which can (and should) provide text alternates and other information to enhance accessibility as appropriate. .

The spine need not include references to every one of the manifest’s item elements that reference OEB documents, because there are means other than the spine for accessing documents in the publication. For example, hypertext links may provide access to documents not in the spine, as may tours and guides (see below).

For example,

In the above example, suppose the document referenced by ID "c1" is being viewed by a reader. When the end of that document is reached, the next document in linear order would be that referenced by ID "C2". Document "c1" might also have hypertext links to locations in another file such as the "footnotes". Such a file must be listed in the manifest, but need not be named by any itemref of the spine. If a reader follows the hyperlink in "c1" to "footnotes", and the end of that file is reached, then no successor in linear order is defined by this specification.

2.5 Tours

Much as a tour-guide might assemble points of interest into a set of sightseers’ tours, a content provider may assemble selected parts of a publication into a set of tours to enable convenient navigation.

An OEB package may, but need not, contain one tours element, which in turn contains one or more tour elements. Each tour must have a title attribute, intended for presentation to the user. Reading systems may use tours to provide various access sequences to parts of the publication, such as selective views for various reading purposes, reader expertise levels, etc. Because reading systems are not required to implement tour support, content providers should also provide other means of accessing content referenced from tours.

Each tour element contains one or more site elements, each of which must have an href attribute and a title attribute. The href attribute must refer to an OEB document included in the manifest, and may include a fragment identifier as defined in section 4.1 of RFC 2396 (see http://www.ietf.org/rfc/rfc2396.txt). Each site element specifies a starting point from which the reader may explore freely. The order of site elements is presumed to be significant, and should be used by reading systems to aid navigation.

Example:

2.6 Guide

Within the package there may be one guide element, containing one or more reference elements. The guide element identifies fundamental structural components of the publication, to enable reading system to provide convenient access to them.

Example:

The structural components of the books are listed in reference elements contained within the guide element. These components may refer to the table of contents, list of illustrations, foreword, bibliography, and many other standard parts of the book. Reading systems are not required to use the guide element in any way.

Each reference must have an href attribute referring to an OEB document included in the manifest, and which may include a fragment identifier as defined in section 4.1 of RFC 2396 (see http://www.ietf.org/rfc/rfc2396.txt).

The required type attribute describes the publication component referenced by the href attribute. The values for the type attributes must be selected from the list defined below when applicable. Other types may be used when none of the predefined types are applicable; their names must begin with the string "other.".

The following list of type values is derived from the 13^th edition of the Chicago Manual of Style:

cover the book cover(s), jacket information, etc.

title-page page with possibly title, author, publisher, and other metadata

toc table of contents

index back-of-book style index

glossary glossary

acknowledgements

bibliography

colophon

dedication

epigraph

foreword

loi list of illustrations

lot list of tables

notes

preface

3 HTML/XML Markup Constructs

This section lists all element types included in the OEB document specification. They are drawn from the HTML 4.0 specification found at http://www.w3.org/TR/REC-html40. See also Appendix A, which includes an index of element types and their status in HTML 4.0 and this specification.

3.1 Notational Conventions

This section does not list HTML 4.0 element types that are not supported in OEB documents (the table in Appendix A, however, does show them explicitly and marks them as excluded). For elements that are supported, this section does, however, explicitly indicate attributes that are ruled out. Reading systems may accept the presence of additional attributes (except in valid OEB documents), but need not support their semantics.

The following typographic conventions are used to indicate the status of element types, attributes, and attribute values:

3.1.1 Strikethrough

Attributes and attribute values whose names are struckthrough below are HTML 4.0 constructs that are explicitly not supported by this specification. Reading systems may , but needo not provide default presentation for them. In some cases, the constructs are intended to be permanently obsolete; in other cases, future revisions of this specification may add support for these constructs.

3.1.2 Underline

Elements, attributes, and attribute values whose names are underlined below are additions beyond the HTML 4.0 specification. Specifically:

•	The lowsrc (de facto) attribute on img; and
•	The just (de facto) value for align on various elements (which is, nevertheless, deprecated).

3.1.3 (meaning changed)

Elements, attributes, and attribute values whose names are followed by "(meaning changed)" below have had their semantics altered from those of the HTML 4.0 specification.

3.1.4 (deprecated)

Elements, attributes, and attribute values whose names are followed by "(deprecated)" below are deprecated (that is, permitted but not recommended) in OEB documents. The accompanying text indicates whether they are also deprecated in HTML 4.0. Although reading systems must recognize and support them, future releases of this specification are likely to prohibit them. Most but not all are deprecated in HTML 4.0. All elements, attributes, and attribute values that are deprecated in HTML 4.0 are either deprecated or prohibited by this specification.

3.1.5 <x> </x> versus <x />

Elements that cannot contain subelements or text content are shown with the required empty-element syntax, while others are shown as start- and end-tag pairs. Note the XML documents may not omit start- or end-tags. The supported HTML elements for which this restriction is relevant include: html, body, head, dt, li, p, caption, td, and th.

3.2 Generally Applicable Attributes

HTML 4.0 defines the following four attributes that may be applied to nearly all elements. These attributes are therefore not listed in the following element descriptions, except to note their absence from the few exceptional elements.

3.2.1 id

This attribute is used to give a unique identifier to each element. Values for id must be unique across all elements in a single document, and may consist of the full range of XML name characters. For compatibility with HTML, restricting the id values to the HTML name characters (A-Za-z0-9.-) is recommended.

3.2.2 style

This attribute is included to allow for inline style specification. See the discussion of supported CSS properties elsewhere in this specification.

3.2.3 class

This attribute is included to allow selector-based style specifications. Its value must be a space-separated list of class names. OEB class names are limited to valid HTML 4.0 names, although HTML 4.0 allows arbitrary CDATA.

3.2.4 title

This attribute may be used to provide an "advisory title/amplification" for the element. Reading systems are not required to do anything in particular with its value.

3.3 Rendering on Limited Reading Systems

A number of elements and attributes that are allowed below permit semantics that are not required of all OEB reading systems. For example, some devices may 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 HTML construct, 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 HTML constructs. Some reading systems may choose to express the intent of elements in presentation by closely following web-browser usages – a blank line before a paragraph, but no first-line text-indent, for example. Other reading systems may 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, may present particular elements or entire documents in completely different ways.

3.4 <?xml ?>

An OEB document must begin with the XML processing instruction

<?xml version="1.0" ?>

It is recommended that a character encoding be specified, for example:

<?xml version="1.0" encoding="UTF-16" ?>

3.5 <!DOCTYPE>

A <!DOCTYPE> declaration in a basic OEB document must reference the OEB document DTD, by system and optionally the public identifier. For example:

<!DOCTYPE html PUBLIC
"+//ISBN 0-9673008-1-9//DTD OEB 1.0 Document//EN"
"http://openebook.org/dtds/oeb-1.0/oebdoc1.dtd">

Note that the <!DOCTYPE> declaration must not include a trailing slash, but may include "[ ]" preceding the closing ">". "DOCTYPE" must be in upper case. Also, implementations should normalize whitespace in PUBLIC identifiers in accordance with the rules defined in XML, though the use of non-normalized whitespace in PUBLIC identifiers in OEB documents is prohibited.

3.6 <a> </a>

Marks either the origin or destination for a hypertext link. Note that many browsers by default underline anchors with href attributes, to visually indicate links. Similarly, reading systems will use some sort of highlighting, perhaps some form of underline, to show links. The CSS-property setting text-decoration: none may be used to suppress such highlighting.

3.6.1 name (deprecated)

Used to provide an address to which hypertext links may refer.

Deprecated in HTML 4.0 and in this specification, in favor of the id attribute. HTML 4.0 allows any string as the value of this attribute; this specification limits them to being XML names.

3.6.2 href

Provides a URI to be used as the destination when traversal from the a element is requested. If this URI references a destination that is not an OEB core media type, a fallback must be provided in the manifest to an OEB core media type. If a fallback is not provided in the manifest, content at the end of this link must not be rendered by the reading system.

3.6.3 rel, rev

May be used to indicate the relationship between the document or portion linked, and the current document or portion.

3.6.4 charset, type, hreflang, accesskey, shape, coords, tabindex, onfocus, onblur

Omitted from this specification.

3.7 <area />

3.7.1 shape

The possible values are:

rect The default. Coordinates are left, top, right, bottom values.

circle Coordinates are center x, center y, and radius.

poly Coordinates are x, y pairs for successive points.

default The default type, rect, can also be set explicitly.

3.7.2 coords

Comma-separated list of lengths, as integer coordinates or percentages. The values are interpreted according to the specific shape value.

3.7.3 href

Provides a URI to be used as the destination when traversal from this area is requested (for example by clicking within a hotspot). If this URI references a destination that is not an OEB core media type, a fallback must be provided in the manifest to an OEB core media type. If a fallback is not provided in the manifest, the destination resource must not be rendered by the reading system. A non-null value for the alt attribute of this element will be considered acceptable fallback.

3.7.4 nohref

If set to nohref="nohref", indicates that the area isn’t "hot," effectively "punching a hole" in a larger hot region.

3.7.5 alt

Should be used to provide an alternative textual representation for the hot-spot, accessible to print-disabled users.

3.7.6 tabindex, accesskey, onfocus, onblur

Omitted from this specification.

3.8 <b> </b>

The b tag is commonly used in HTML documents. Use of CSS font-weight:bold or the HTML strong tag is preferable.

3.9 <base />

Used in resolving links from OEB documents.

3.9.1 href

Provides a URI to be used as the basis for relative URIs elsewhere in the document.

3.9.2 id, style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.HTML 4.0 and this specification exclude these general attributes from this element.

3.10 <big> </big>

3.11 <blockquote> </blockquote>

3.11.1 cite

This optional attribute provides a URI for the source of the quoted material.

3.12 <body> </body>

This element defines a container for OEB content. It is assumed, in formatting, that its default rendering is consistent with the CSS property page-break-before:always, but may be overridden by an appropriate stylesheet declaration.

3.12.1 bgcolor (deprecated)

Deprecated in HTML 4.0 and in this specification, in favor of CSS background-color equivalent. See section 4.1, the CSS color and background-color properties, for discussion of acceptable values.

3.12.2 text (deprecated)

Deprecated in HTML 4.0 and in this specification, in favor of CSS color equivalent. See section 4.1, the CSS color and background-color properties, for discussion of acceptable values.

3.12.3 link, vlink, alink, background

This specification does not require reading systems to support color control of link anchors or background bitmaps. These attributes are deprecated in HTML 4.0 and omitted from this specification.

3.12.4 onload, onunload

Omitted from this specification.

3.13 <br />

3.13.1 clear (deprecated)

The possible values are:

none (default)

left

right

all

Deprecated in HTML 4.0, in favor of CSS clear property.

3.14 <caption> </caption>

When present, the caption element’s text should describe the nature of the table.

3.14.1 align

Omitted from this specification.

3.15 <center> </center> (deprecated)

Equivalent to <div align="center">. Deprecated in HTML 4.0 and in this specification.

3.16 <cite> </cite>

Citations of other sources.

3.17 <code> </code>

Computer program fragments.

3.18 <dd> </dd>

Definition description.

3.19 <dfn> </dfn>

Inline definitions, such as the first instance of a definition.

3.20 <div> </div>

3.20.1 align (deprecated)

See section 3.25.1, h1, for additional discussion.

3.21 <dl> </dl>

Definition list.

3.21.1 compact

See section 3.58.2, ul, for additional discussion.

3.22 <dt> </dt>

Definition term.

3.23 <em> </em>

Emphasis, typically formatted like i.

3.24 <font> </font> (deprecated)

The font element is deprecated in HTML 4.0 and this specification, with its functionality replaced by CSS equivalents.

3.24.1 size (deprecated)

3.24.2 color (deprecated)

See section 3.12.1, the bgcolor and text.attributes of the body element, for additional discussion.

3.24.3 face (deprecated)

3.25 <h1> </h1> through <h6> </h6>

3.25.1 align (deprecated)

The possible values are:

left

center

right

justify

Deprecated in favor of the equivalent CSS construct, text-align.

3.26 <head></head>

3.26.1 profile

Omitted from this specification.

3.26.2 id, style, class, title

HTML 4.0 excludes these general attributes from this element.

3.27 <hr />

3.27.1 align (deprecated)

The possible values are:

left

right

center

Deprecated in favor of the equivalent CSS construct, text-align.

3.27.2 noshade

Deprecated in HTML 4.0, omitted from this specification.

3.27.3 size (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS height .

3.27.4 width (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS width. Value is specified in pixels or percentage.

3.28 <html> </html>

This element is required in OEB documents.

3.28.1 id, style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.

3.29 <i> </i>

The i tag is commonly used in HTML documents. Use of CSS fontstyle:italic or the HTML em tag is preferable.

3.30 <img />

A reference to an image to be displayed inline. This element may only be used to refer to images of OEB core media types (PNG and JFIF [JPEG]). Inline references to non-core media types require specification of alternate (fallback) rendering. The object element provides a general fallback mechanism by which all reading systems may locate an alternate of a core media type, and is the preferred mechanism for including non-core media types. However, a non-null value for the alt attribute is also considered an adequate fallback.

3.30.1 src

Images must be of type PNG (see http://www.ietf.org/rfc/rfc2083.txt) or JFIF (see ISO/IEC 10918-1:1994(E) and http://www.igd.fhg.de/icib/it/iso/is_10918-1/gen.html).

3.30.2 alt

Should be used to provide a non-graphical alternative to a graphic. This is crucial to accessibility of documents to print-disabled users, as well as for use on very low-resolution display devices. See http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/#gl-provide-equivalents for further information on the use of this and related accessibility attributes.

3.30.3 longdesc

Value should be a URI pointing to a long description, typically more detailed than, but complementary to, alt. Use of this attribute is strongly recommended because it can greatly enhance accessibility for print-disabled users.

3.30.4 align (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS float and vertical-align properties.

The possible values are:

top

middle

bottom

left

right

3.30.5 width (deprecated)

Deprecated in this specification, though not in HTML 4.0, in favor of CSS width property.

3.30.6 height (deprecated)

Deprecated in this specification, though not in HTML 4.0, in favor of CSS height property.

3.30.7 border (deprecated)

Deprecated in HTML 4.0 and this specification.

Pixel width for image border. The value 0 is particularly useful for img elements embedded in a elements, because typical HTML browsers apply a default border when rendering image-based hypertext links. This specification requires only that values of 0 and 1 be respected. Values greater than 1 may be mapped by the reading device to any smaller non-zero value.

3.30.8 hspace (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS margin mechanisms.

Reserves equal amount of whitespace to the left and right of an image.

3.30.9 vspace (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS margin mechanisms.

Reserves equal amount of whitespace above and below an image.

3.30.10 usemap

Points to a client-side map; the value of usemap refers to the map element’s name or id attribute (see map 3.34).

3.30.11 ismap

Omitted from this specification. In HTML 4.0, value is a reference to a server-side map for defining hotspots.

3.31 <kbd> </kbd>

The indication of text to be entered by a user, often used in software manuals.

3.32 <li> </li>

3.32.1 type

Deprecated in HTML 4.0 and omitted from this specification.

3.32.2 value

Deprecated in HTML 4.0 and omitted from this specification.

3.33 <link />

In HTML the link element allows for specification of various relationships with other documents. Reading systems must recognize external stylesheet references specified via the link element. See section 1.4.4.

3.33.1 href

Provides the URI of a linked object.

3.33.2 rel, rev

Indicates the relationship to the linked document. Reading systems must support rel="stylesheet" and support rel="alternate stylesheet". See the HTML 4.0 specification.

3.33.3 media

May be used to indicate the intended destination for style information, but may be ignored by reading systems.

3.33.4 type

This required attribute is used to specify the stylesheet language (e.g. "text/x-oeb1-css" or "text/css").

3.33.5 charset, hreflang

Omitted from this specification.

3.34 <map> </map>

Contains area elements defining client-side hotspots for an image.

3.34.1 id

A required unique identifier for the map. See section 3.6, the a element, for restrictions on the characters permitted in names.

3.34.2 name (deprecated)

A unique identifier for the map. Deprecated in HTML 4.0 and in this specification, in favor of the id attribute; the name attribute is now optional. See section 3.6, the a element, for restrictions on the characters permitted in names.

3.35 <meta />

See the HTML 4.0 specification for further information.

For information regarding publication description (Dublin Core) metadata, see Chapter 2 of this specification.

3.35.1 name

3.35.2 content

3.35.3 scheme

3.35.4 http-equiv

Omitted from this specification.

3.35.5 id, style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.

3.36 <object></object>

The object element is the preferred method for generic object inclusion. When adding objects whose data media type is not drawn from the core OEB media type list or which references an object implementation using the classid attribute, the object element must specify fallback information for the object, such as another object, an img, or descriptive text.

3.36.1 archive

See the HTML 4.0 specification for details.

3.36.2 classid

The URI of an implementation for the object. Conformant reading systems are not required to render objects that use external implementations, although they may do so.

3.36.3 codebase

The base path to be used for relative URIs in the classid attribute.

3.36.4 codetype

Specifies the MIME media type of the implementation referenced in classid.

Note: the type must match the MIME media type specified in the publication’s manifest.

3.36.5 data

The URI of the data for this object.

3.36.6 type

The MIME media type of the information referenced by the data URI.

Note: the type must match the MIME media type specified in the publication’s manifest.

3.36.7 align, height, width, border, hspace, vspace (deprecated)

Deprecated. See section 3.30, img, for additional discussion.

3.36.8 usemap

Refers to a client-side map element by its name attribute’s value, in order to define hotspots.

3.36.9 declare, standby, tabindex, name

Omitted from this specification.

3.37 <ol> </ol>

3.37.1 type (deprecated)

1, a, A, i, I Specifies a form of letters or numerals to use for the list items.

Deprecated in HTML 4.0 and this specification, in favor of CSS list-style-type .

3.37.2 start

Deprecated in HTML 4.0 and omitted from this specification.

3.37.3 compact

Omitted from this specification.

3.38 <p> </p>

3.38.1 align (deprecated)

See section 3.25, h1, for additional discussion.

3.39 <param />

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

3.39.1 name

The name of a parameter used by the parent object.

3.39.2 value

The value of the parameter.

3.39.3 valuetype

The type of data stored in value:

data The default. The data stored in value is passed to the object as a string.

ref The data is a URI, and is passed to the object as specified, without being resolved.

object An identifier that refers to an object declaration in the same document. The identifier must be the value of the id attribute set for the declared object s element.

3.39.4 type

Used when the valuetype is "ref". Specifies the MIME media type of the data a reading system should expect at the given URI.

3.39.5 style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.

3.40 <pre> </pre>

Preformatted text to be rendered in a monospace font, such as program listings.

3.40.1 width

Deprecated in HTML 4.0 and omitted from this specification.

3.41 <q> </q>

Short inline quotation (see also section 3.11, blockquote).

3.41.1 cite

Provides a URI for the source of the quoted material. Reading systems are not required to make use of this attribute.

3.42 <s> </s> (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of the CSS text-decoration:line-through property.

3.43 <samp> </samp>

Identifies the contents as program output, scripts, etc.

3.44 <script> </script>

Reading systems must not render the textual content of the script element, but may choose to execute the script itself. To render the textual content of the script element, this specification recommends using the CSS 1 display property to achieve this effect instead.

3.44.1 charset, type, src, defer, event, for

Omitted from this specification.

3.44.2 id, style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.

3.45 <small> </small>

3.46 <span> </span>

Particularly useful for associating CSS style information with inline content.

3.47 <strike> </strike> (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of the CSS text-decoration:line-through property.

3.48 <strong> </strong>

Strong emphasis, typically formatted like b.

3.49 <style> </style>

See section 1.4.4.

3.49.1 type

The value must be:

Text/x-oeb1-css

OEB documents’ embedded style information must always use only the CSS subset defined in this specification.

3.49.2 media

Omitted from this specification.

3.49.3 id, style, class

HTML 4.0 and this specification exclude these general attributes from this element.

3.50 <sub> </sub>

3.51 <sup> </sup>

3.52 <table> </table>

Reading systems may exercise great flexibility in laying out tables which would otherwise be too large to fit on the display.

3.52.1 align (deprecated)

The possible values are:

left CSS equivalent is float:left

right CSS equivalent is float:right

center CSS equivalent is to enclose the table in a div element and set text-align:center

3.52.2 width

3.52.3 border

According to HTML 4.0, any number of pixels may be specified. This specification only requires that values of 0 and 1 be respected. Values greater than 1 may be mapped by the reading system to any smaller non-zero value.

3.52.4 cellspacing, cellpadding

3.52.5 bgcolor (deprecated)

See section 3.12.1, the bgcolor attribute of body, for additional discussion.

3.52.6 summary

A text summary of the table’s purpose and/or structure, such as for speech output. This can be crucial in making documents accessible to print-disabled users.

3.52.7 frame, rules

Omitted from this specification.

3.53 <td> </td> or <th> </th>

3.53.1 nowrap (deprecated)

Deprecated in HTML 4.0 and this specification. The non-deprecated alternative is to replace each run of whitespace with a single non-breaking space. Reading systems may choose to override this setting in cases where the default rendering of a particular table is bigger than the display surface.

3.53.2 rowspan, colspan

3.53.3 align

The possible values are:

left

center

right

justify

3.53.4 valign

The possible values are:

top

middle

bottom

3.53.5 width (deprecated), height (deprecated)

Deprecated in HTML 4.0 and this specification. In pixels. Instead, use the CSS width and height to set value in pixels.

3.53.6 bgcolor (deprecated)

See section 3.12.1,the bgcolor attribute of body, for additional discussion.

3.53.7 abbr

An abbreviated form of the content, particularly to enhance accessibility for the print-disabled user, but also useful for other purposes such as rendering on small displays.

3.53.8 axis, headers, scope

Omitted from the specification.

3.54 <title> </title>

See chapter 2 for information on the relationship between the HTML title and the Dublin Core metadata Title.

3.54.1 id, style, class, title

HTML 4.0 and this specification exclude these general attributes from this element.

3.55 <tr> </tr>

3.55.1 align

Omitted from this specification.

3.55.2 valign

The possible values are:

top

middle

bottom

3.55.3 bgcolor (deprecated)

See section 3.12.1, the bgcolor attribute of body, for additional discussion.

3.56 <tt> </tt>

Monospace display inline.

3.57 <u> </u> (deprecated)

Deprecated in HTML 4.0 and this specification, in favor of CSS text-decoration:underline.

3.58 <ul> </ul>

3.58.1 type

Deprecated in HTML 4.0 and omitted from this specification. Reading systems need support only one form of bullet, preferably disc.

3.58.2 compact

Deprecated in HTML 4.0 and omitted from this specification.

3.59 <var> </var>

Identifies a mention of a variable or program argument.

4 CSS Constructs

This discussion refers to the CSS 1 and CSS 2 specifications, which can be found at http://www.w3.org/TR/REC-CSS1/ and http://www.w3.org/TR/REC-CSS2/ respectively.

This specification requires support for only three kinds of CSS selectors. Specifically, those of the form

.classname {}
TAGNAME {}
TAGNAME.classname {}

This specification does not require support for id-based selectors, or selectors that qualify element types based on the element types of their containing elements.

Multiple selectors may be combined with commas, as in

h1, h2, h3, h4, h5, h6 {text-indent: 0em}

All non-zero coordinate and size values must have specified units. All units defined by CSS 1 and 2 are supported:

px Pixels

ex x-height of current font

em m-width of current font

pt Points

in Inches

cm Centimeters

mm Millimeters

pc Picas

Where percentage units are supported, informative text below explains their interpretation, which is as defined in the CSS specifications.

This specification does not list CSS properties omitted from this specification. It does identify, using the previous convention of strike-through, CSS 1 property values that are omitted from this specification. It underlines extensions beyond CSS 2. And it uses "(meaning changed)" to denote changes to the functionality of a property or keyword already defined in CSS.

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 not, however, required to support every distinction; the main example is that they are not required to render borders or to float anything but the specific elements img and table.

4.1 background-color: and color:

Some reading devices do not support colors, or even gray-scale. Use of colors other than white or black may not produce useful renderings on all reading devices.

Current browsers support a host of keyword color names. HTML 4.0 defines 16 named colors, as well as numeric values. OEB stylesheets may use all CSS 1 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).

As with other names in this specification and in XML, these names are case-sensitive (unlike in HTML, which allows mixed case).

This specification requires control of some aspects of borders, if only to provide non-deprecated alternatives to the <table border="n"> and <img border="n" /> attributes. Of the twelve border properties defined by CSS 1, this specification includes only the border property. It can be used to set a single combination of style, width, and color values for all four borders of an element. This specification also does not require rendering support for color borders.

Reading systems must recognize all of the following style keywords, but may choose to map any style other than none to solid, consistent with the rules for the "CSS 1 core." Reading systems need not render borders except for img, object, and table.

A reading system need not render three different widths for the three keyword values. For example, it may map non-zero absolute widths to 1 pixel.

Note: Reading systems must recognize the same set of color values for border as for background-color: and color: (see section 4.1 above), but need not actually distinguish them all in rendering.

Provide support equivalent to the deprecated br clear attribute. The possible values are:

CSS 1 defines various values for this property, with CSS 2 adding more. Reading systems must respect the CSS 1 values block, inline, and none.

This specification also defines two new values: oeb-page-head and oeb-page-foot. Any content meant for presentation as a page-header or page-footer should be marked up and assigned these values via the display property.

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.

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 element below would become the page header or footer as soon as nothing preceding the containing div is displayed:

<div>
<myhead style="display: oeb-page-head">The OEB Spec: Introduction</myhead>
<h2>Introduction</h2>
<p>…

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.

block Indicates the element is to be formatted as a block, with line-breaks at both ends.

inline Indicates the element is to be formatted without forcing line-breaks at the ends.

Note: CSS enables a subtle mechanism for controlling whether or not a page-header should be displayed inline when rendered by existing browsers. The most straightforward construct:

will render in an existing browser, for the browser will not recognize, and therefore ignore, the display: oeb-page-head setting. On the other hand,

will not render in an existing browser. The browser will respond to display: none, ignore the display: oeb-page-head, and suppress formatting and rendering of the div.

Although CSS 1 applies this to all elements, enabling any element to be extracted from inline flow, with normal text wrapping around. Reading systems need not actually float elements other than img, object, and table. The possible values are:

Accepts a comma-separated list of family names, in order of preference. CSS defines five generic font family names, three of which reading systems must support :

Reading systems must accept the seven named font-sizes, as well as the forms for stepping one size (among the seven) larger or smaller than surrounding text. As discussed under <font size="">, there is no requirement that any given reading device actually render using seven distinct sizes.

Reading devices may provide means to change the mapping between the 7 named font-sizes and physical font sizes. Font-sizes specified with absolute units are presumed not to change size during normal operation (although they may do so in modes focused on universal access for the vision impaired). Content authors should avoid specifying absolute physical font sizes; doing so deprives the user of one of the significant benefits of an electronic book – user control over relative font size.

Reading systems are free to treat italic and oblique synonymously; if a system sees either, it may apply either form (many font families provide only one of the two).

and omits the others (reading systems may accept these values, and are free to render them more simply, such as using only two degrees of boldness):

This property sets the distance between the baselines of two adjacent lines. It accepts the values "normal", a number, or a length. Negative values are not allowed.

When "normal" is specified, CSS recommends that it function like a numeric value in the range of 1.0 to 1.2.

When a numerical value is specified, the line height is the font size of the current element multiplied by that value. This differs from a percentage value in the way it inherits: when a numerical value is specified, child elements will inherit the factor itself, not the resultant value (as is the case with percentage and other units).

If a line of text contains sections with different ’line-height’ values (because there are inline elements on the line), then each of those sections has its own half-leading above and below. The height of the line-box is from the top of the highest section to the bottom of the lowest one. Note that the top and bottom do not necessarily correspond to the tallest element, since elements can be positioned vertically with the ’vertical-align’ property. To form a paragraph, each line-box is stacked immediately below the previous line.

Note that any padding, border or margin above and below non-replaced inline elements does not influence the height of the line. In other words: if the ’line-height’ is too small for the chosen padding or border, it will overlap with text on other lines.

Replaced elements (e.g. images) on the line can make the line-box bigger, if the top of the replaced element (i.e., including all of its padding, border and margin) is above the tallest text section, or if the bottom is below the lowest.

This property delivers the functionality of ordered and unordered lists, and their type attributes. CSS 2 introduces additional values beyond those listed below, none of which are currently supported by this specification.

Applies only to the predefined HTML 4.0 list types at this time, because the display:list-item value is not presently supported.

The value must be a length or a percentage. Percentage is relative to the width of the closest block-level ancestor. Reading systems are not required to support the value auto, which sets the value to that of the opposite margin.

Note that adjacent top and bottom margins coalesce. If a paragraph with margin-bottom: m px is followed by another with margin-top: n px, then the resulting whitespace is the greater of m and n, as opposed to their sum.

Including this property eliminates the need for many uses of the align attribute. The possible values are:

The value must be a length or a percentage. Percentage is relative to the parent element’s width.

Although CSS applies this to any inline elements reading systems need only support it for images to achieve the functionality of <img align="top" />, <img align="middle" />, and <img align="bottom" />.

The value must be a length or a percentage. Percentage is relative to the width of the parent element. Reading systems are not required to support the value auto.

Reading systems are free to treat left and right as always. The possible values are:

left Force one or two page breaks so that the following content begins on a left-hand page.

right Force one or two page breaks so that the following content begins on a right-hand page.

Note that this specification does not require support for the page-break-after: property.

Used to implement "keep-together" functionality. With page-break-inside:avoid, the entire element would be moved to a new page rather than broken across a page boundary. Explicit page breaks, as specified by page-break-before:always, take precedence over page-break-inside:avoid.

Note that the page-break-inside property is not supported in all current HTML browsers.

This specification allows use of this special property pending development of a CSS solution. It is suggested that this feature be accessed solely through the use of external stylesheets (not inline) so that a future standard method for accessing this functionality can be easily substituted. The possible values are:

auto Reading device decides on optimal number of columns in which to render the text, considering available width, font sizes, or any other metrics it considers relevant for readability.

1 Reading device should render in one column, regardless of the amount of horizontal space available to display the text.

Reading systems are free to support integer values other than 1, or may map them to 1.

The following table lists all the relevant HTML element type names alphabetically, along with their status in HTML 4.0 and OEB 1.0. Information about HTML 4.0 is based on the HTML 4.0 element table (http://www.w3.org/TR/REC-html40/index/elements.html). The status is marked as follows:

4.0: Blank for the Strict DTD, "F" for the Frameset DTD; "L" for the Loose DTD, "NOT" if not in HTML 4.0 at all (3.2 only); "D" when deprecated (all "L" cases except iframe).

Element Type	Empty	4.0	OEB	Description
a			+	anchor
abbr			-	abbreviated form
acronym			-	acronym
address			-	information on author
applet		L, D	-	Java applet
area	E		+	client-side image map area
b			+	bold text style
base	E		+	document base URI
basefont	E	L, D	-	base font size
bdo			-	I18N BiDi over-ride
big			+	large text style
blockquote			+	long quotation
body			+	document body
br	E		+	forced line break
button			-	push button
caption			+	table caption
center		L, D	D	justification control
cite			+	citation
code			+	computer code fragment
col	E		-	table column
colgroup			-	table column group
dd			+	definition description
del			-	deleted text
dfn			+	instance definition
dir		L, D	-	directory list
div			+	generic language/style container
dl			+	definition list
dt			+	definition term
em			+	emphasis
fieldset			-	form control group
font		L, D	D	local change to font
form			-	interactive form
frame	E	F	-	subwindow
frameset		F	-	window subdivision
h1			+	heading
h2			+	heading
h3			+	heading
h4			+	heading
h5			+	heading
h6			+	heading
head			+	document head
hr	E		+	horizontal rule
html			+	document root element
i			+	italic text style
iframe		L	-	inline subwindow
img	E		+	Embedded image
input	E		-	form control
ins			-	inserted text
isindex	E	L, D	-	single line prompt
kbd			+	text to be entered by the user
label			-	form field label text
legend			-	fieldset legend
li			+	list item
link	E		+	a media-independent link
(listing)		NOT	-	(program listing, 3.2 only)
map			+	client-side image map
menu		L, D	-	menu list
meta	E		+	generic meta-information
noframes		F	-	alternate content container for non frame-based rendering
noscript			-	alternate content container for non script-based rendering
object			+	generic embedded object
ol			+	ordered list
optgroup			-	option group
option			-	selectable choice
p			+	paragraph
param	E		+	named property value
(plaintext)		NOT	-	(plaintext, 3.2 only)
pre			+	preformatted text
q			+	short inline quotation
s		L, D	D	strike-through text style
samp			+	program output, scripts, etc.
script			+	script statements
select			-	option selector
small			+	small text style
span			+	generic language/style container
strike		L, D	D	strike-through text
strong			+	strong emphasis
style			+	style info
sub			+	subscript
sup			+	superscript
table			+
tbody			-	table body
td			+	table data cell
textarea			-	multi-line text field
tfoot			-	table footer
th			+	table header cell
thead			-	table header
title			+	document title
tr			+	table row
tt			+	teletype or monospaced text
u		L, D	D	underlined text style
ul			+	unordered list
var			+	instance of a variable or program argument
(xmp)		NOT	-	(example, 3.2 only)