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Matt Garrish and Markus Gylling

EPUB 3 Best Practices

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ISBN: 978-1-449-32914-3

[LSI]

EPUB 3 Best Practices

by Matt Garrish and Markus Gylling

Copyright © 2013 Matt Garrish and Markus Gylling. All rights reserved.

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February 2013: First Edition

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2013-01-23 First release

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While every precaution has been taken in the preparation of this book, the publisher and authors assume

no responsibility for errors or omissions, or for damages resulting from the use of the information contained

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Table of Contents

Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

1. Package Document and Metadata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Vocabularies 2

The Default Vocabulary 3

The Reserved Vocabularies 3

Using Other Vocabularies 4

The All-Powerful meta Element 5

Publication Metadata 7

The Package Document Structure 8

The metadata Element 9

Identifiers 11

Types of Titles 14

The Manifest and Spine 15

The manifest and Fallbacks 16

The spine 17

Document Metadata 19

Links and Bindings 20

Metadata for Fixed Layout Publications 22

The Container 22

2. Navigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

The EPUB Navigation Document 26

Building a Navigation Document 29

Repeated Patterns 31

Table of Contents 35

Landmarks 41

Page List 44

Extensibility 45

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Adding the Navigation Document 46

Embedding as Content 47

Hiding Lists 48

Styling Lists 49

The NCX 50

3. Content Documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Terminology Refresher 53

XHTML 55

New in HTML5 56

EPUB Support Gotchas 62

DTDs Are Dead 63

Linking and Referencing 64

Content Chunking 67

epub:type and Structural Semantics 68

Adding Semantics 70

Multiple Semantics 72

MathML 72

SVG 78

Fixed Layouts 80

Covers 85

Styling 87

EPUB CSS Profile 88

CSS 2.1 88

CSS3 91

Ruby 96

Headers and Footers 97

Alt Style Tags 99

CSS Resets 102

Fallback Content 102

Manifest Fallbacks 103

Content Fallbacks 105

The epub:switch element 107

Bindings 112

4. Font Embedding and Licensing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Why Embed Fonts? 118

Maybe You Shouldn’t 118

Maybe You Should 122

Font Embedding in EPUB 3 130

How to Embed Fonts 131

Add the Font to Your EPUB Package 132

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Include the File in the EPUB Manifest 132

Reference the Font in the EPUB CSS 133

Obfuscating Fonts 134

Subsetting a Font 137

Licensing Fonts for Embedding in EPUB 138

Use an Open Font 139

Contact the Foundry Directly 139

5. Multimedia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

The Codec Issue 142

The Media Elements 144

Sources 145

Control 153

Posters 155

Dimensions 156

The Rest 157

Timed Tracks 157

Fallbacks 162

Alternate Content 163

Triggers 165

6. Media Overlays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

The EPUB Spectrum 174

Overlays in a Nutshell 176

Synchronization Granularity 177

Constructing an Overlay 178

Sequences 180

Parallel Playback 181

Adding to the Container 184

Styling the Active Element 185

Structural Considerations 186

Advanced Synchronization 187

Audio Considerations 188

7. Interactivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

First Principles: Interaction Scope and Design 192

Progressive Enhancement 192

Procedural Interaction: JavaScript 193

JavaScript in EPUB 2 193

The EPUB 3 epubReadingSystem Object 193

Inclusion Models 197

Ebook State and Storage 199

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Identifying Scripted Content Documents 199

Animation and Graphics: Canvas 200

Best Practices in Canvas Usage 201

Canvas in a Nonscripted Reading System 202

Object 203

Other Graphical Interaction Models 204

Accessibility and Scripting Summary 204

8. Global Language Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

Characters and Encodings 206

Unicode 206

Declaring Encodings 207

Private Characters 208

Names 209

Specifying the Natural Language 211

Vertical Writing 212

Writing Modes 213

Page Progression Direction 215

Global Direction 220

Content Direction 221

Ruby and Emphasis Dots 222

Ruby 222

Emphasis Dots 224

Line Breaks, Word Breaks, and Hyphenation 226

Itemized Lists 227

9. Accessibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

Accessibility and Usability 230

Fundamentals of Accessibility 232

Structure and Semantics 233

Data Integrity 235

Separation of Style 237

Semantic Inflection 238

Language 239

Logical Reading Order 239

Sections and Headings 241

Context Changes 244

Lists 245

Tables 246

Figures 249

Images 250

SVG 253

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MathML 254

Footnotes 255

Page Numbering 256

Styling 258

Avoiding Conflicts 258

Color 258

Hiding Content 260

Emphasis 260

Fixed Layouts 261

Image Layouts 262

Mixed Layouts 265

Text Layouts 266

Interactive Layouts 266

Scripted Interactivity 267

Progressive Enhancement 267

WAI-ARIA 269

Canvas 280

Metadata 281

10. Text-to-Speech (TTS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

PLS Lexicons 287

SSML 292

CSS3 Speech 297

11. Validation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

epubcheck 304

Installing 304

Running 305

Options 308

Reading Errors 313

Beyond the Command Line 314

Web Validation 314

Graphical Interface 316

Commercial Options 316

Understanding Errors 317

Common XML Errors 318

Container Errors 321

Package Validation 323

Content Validation 326

Style 329

Scripting 329

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Accessibility 330

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

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Preface

When I first wrote What Is EPUB 3? in the summer of 2011, it was envisioned as both

a brief standalone piece that would orient people to the new EPUB 3.0 revision the

International Digital Publishing Forum (IDPF) was about to release and also as an in‐

troduction to what we hoped would evolve into a larger best practices guide—the one

you’re reading now.

You’ll find that book distilled down to its bare essentials in this book’s introduction, but

if you are new to EPUB, there is much information put into that original guide that is

helpful to know before tackling this one, so if I can recommend some advance reading,

it would be to grab a copy of that ebook and give it a skim. If you’re not familiar with

EPUBs generally, or what’s changed from 2 to 3, it’ll help give you a general view of the

big picture before launching into the details that we’ll be covering here. It’s only a small￾chapter-length in size, too (and free!), so it won’t take you long to get through, and it

will give you a condensed perspective on what an EPUB is.

This guide instead delves right into the EPUB container and walks you through best

practices as they relate to production of your publications; you’ll find a bit of a mixture

of practices and guidance on how to use EPUB technologies. You don’t necessarily have

to know the technology of publishing EPUBs inside and out to find value here, nor do

you have to be a programmer or tech geek, but this book is for the ebook practitioner.

In planning out this guide, one of the challenges was trying to keep straight where the

boundaries are between EPUB 3 and the technologies it combines under its format

umbrella. Can a single book about EPUB 3 best practices try to detail every nuance of

HTML5, CSS3, JavaScript, MathML and SVG, just to pick out some of the prime content

document technologies? The answer should be obvious, considering the volume of ma‐

terial that’s already been written on those subjects.

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What we’ve tried to do in this guide is find the key areas of overlap between those

technologies as they relate to publishing. You’re going to find a lot of discussion about

all of the features just listed, and more, but if you’re just getting started with the tech‐

nologies used in EPUBs this book will be more of a starting point on your journey. You

will learn about potential issues when scripting in the reading system environment, for

example, but you won’t find a tutorial on the JavaScript language.

Each of the chapters in this book deals with a unique aspect of the creation and distri‐

bution process. There is no assumption that you’re familiar with the entire format, be‐

cause the production of EPUBs often involves expertise from a number of different

functional areas. The people responsible for ensuring the technology of your ebooks

probably aren’t going to be the same people who are responsible for the metadata. The

authors and editors creating the content are likewise not going to be the people bundling

and distributing the ebook. So although the book will move over EPUB 3 in a linear

fashion, and can be read from cover to cover to learn about production as a whole, each

chapter is also intended to be readable in isolation, with pointers forward and back as

necessary.

And although we hope you’ll implement all the best practices you can, the book is not

designed to be a checklist to content conformity, and is not written as such. Everyone

produces using different methods, and everyone has to work within the constraints of

their production workflows, so we’ve tried hard not to target specific processes or read‐

ing systems but stick to the ultimate outcome. If you can’t implement every accessibility

practice, for example, the hope is that at least you’ll understand where, and how, you

can improve later on down the road.

This guide also isn’t intended to be the final word on EPUB, as EPUB is always evolving.

It’s about preparing you for producing EPUB 3 content using all the features it makes

available, helping you avoid known pitfalls, and giving you a heads up on the issues

you’ll face. If successful, it will also hopefully enlighten you to why the specification is

defined the way that it is. A specification is just an artifact of agreement on how to

implement a technology, after all. It tells you what the creators decided you must and

should and may do—and not do—but specifications don’t spend time retelling you the

story of why.

It doesn’t mean you’ll agree with all the decisions that were made, but specifications by

nature portray a myth of homogeneity. It’s the discussions and debate that continue

around EPUB that keep it at the forefront of ebook technologies.

If we’ve done our job writing this book, you should not have new ideas for your own

production, but be well equipped to join in the discussions on the future.

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The Future

By the time this book comes out, the EPUB 3 specification will be more than a year old.

It’s hard to believe how fast time flies, but it’s not surprising that technology is only just

catching up to the standard. That was a goal of the revision after all: to position the

specification so that features and best practices could be defined ahead of the pack

instead of trying to constantly play the catch-up game.

The modular nature of the specification has also proven its worth. Since the specification

was published in October 2011, IDPF subgroups have published two new documents:

fixed layouts and advanced adaptive layouts. Work on grammars for marking up indexes

and dictionaries has been ongoing since the beginning of 2012, and a new group dealing

with hybrid layouts is also in the process of being chartered. The IDPF is continuing to

work with its members to evolve the standard to meet their needs; it’s not sitting on its

laurels or creating a format by fiat.

Another major revision of the standard is not on the horizon at this point, but minor

revisions are anticipated to add new CSS functionality, fix bugs, and see if consensus

can be found on open issues like codecs and metadata. A new minor revision is expected

to begin as this book gets readied for print, which will effect the information in this

guide, but it’s anticipated only for the positive.

You may have RDFa and microdata for content documents by the time you read this,

for example, or at least a firm promise of them. Fixed layout support could be stronger

if the information document it’s currently defined in gets rolled into the main specifi‐

cation. The HTML5 landscape should be clearer, too, as the W3C pushes to finalize the

standard by 2014. EPUB 3 itself also is hoped to become an ISO Technical Specification

during the process.

But don’t worry that this means you’re going to be fed lots of point-in-time ideas. The

areas of instability are not that numerous, and the practices that exist solely to deal with

them are clearly marked. The point of this book is to look at the core of the standard,

so the information should stand for as long as EPUB 3s are being produced.

And even as we began wrapping up this book, a new project to create a conformance

test suite for reading systems was announced, which will help standardize rendering

across reading systems, more and more of which are appearing that support EPUB 3

content. In natural step, publishers are also announcing their plans to start releasing

content (the Hachette Book Group, for example).

EPUB 3 is here, now, in other words.

But we’re not here for long-winded introductions. Let’s get on with the show!

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How to Use This Book

Although you can read this book cover to cover, each chapter contains information

about a unique aspect of the EPUB 3 format allowing them to also be read in isolation.

To simplify jumping through the content, here’s a quick summary of the information in

each:

Introduction

The introduction provides a brief, high-level overview of the EPUB format and

specifications. If you’re coming to this book with no background in EPUB produc‐

tion, this chapter will get you grounded before you head into the details.

Chapter 1: Package Document and Metadata

The first chapter introduces the package document at the heart of every EPUB and

walks you through the process of adding publication metadata. The structure of the

package document is reviewed, as is the required publication metadata. The new,

flexible model for adding metadata to publications via meta elements is also

introduced.

Chapter 2: Navigation

This chapter details the new EPUB navigation document, including how to con‐

struct the required table of contents and optional landmarks and page list navigation

aids. It also shows how the document can now double as content in your publication,

removing the need to have two documents for the same basic function.

Chapter 3: Content Documents

This chapter is more wide-ranging in scope, as it provides a general overview of

content documents. It reviews the new features and requirements of XHTML5, from

the new additions to the core HTML grammar to the inclusion of MathML and

SVG. It also reviews the new epub:type attribute for semantic inflection. EPUB

style sheets, alt style tags and other styling issues are also covered. The chapter

concludes by looking at the various fallback mechanisms at your disposal when

using nonstandard content types.

Chapter 4: Font Embedding and Licensing

The ability to embed fonts allows rich typography in EPUBs. This chapter looks at

the technical details involved in embedding WOFF and OTF fonts, and it also re‐

views the licensing issues to be aware of when you do.

Chapter 5: Multimedia

This chapter looks at the new audio and video elements in HTML5 for embedding

multimedia content in your publications. It covers how to include resources, poster

images, and timed tracks, as well as the issues surrounding the lack of a universal

codec for video. The chapter concludes by looking at epub:trigger elements for

building scriptless user interfaces.

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Chapter 6: Media Overlays

Media overlays is the new technology that enables synchronized text and audio

playback in reading systems, and this chapter reviews the process of creating these

documents. The issues involved in creating overlays for different levels of playback

granularity gets explored, as does the impact on production.

Chapter 7: Interactivity

The addition of scripting in EPUB 3 opens up a whole new dimension in ebooks.

This chapter explores the scripting capabilities supported by the format, the new

epubReadingSystem JavaScript property for querying reading system capabilities,

and also reviews the issues you’ll need to consider when choosing to make your

content dynamic. It also covers the new HTML5 canvas element.

Chapter 8: Global Language Support

To become a truly global standard for ebooks, EPUB 3 was augmented to enable

more than just left-to-right page progressions and horizontal writing styles. This

chapter looks at the mechanics and mechanisms for handling both right-to-left page

progressions and vertical writing styles. It also reviews the new CSS additions that

give greater control over such features as line and word breaking, as well as the use

of ruby annotations.

Chapter 9: Accessibility

Although this book tries to keep a focus on accessibility throughout each chapter,

this one delves into unique accessibility requirements for markup, styling, fixed

layouts, and scripting. WAI-ARIA roles, states and properties are introduced for

dynamic content, as numerous best practices for markup, many drawn from WCAG

2.0.

Chapter 10: Text-to-Speech (TTS)

One of the shortcomings of ebooks for aural readers has been the inability to control

the quality of text-to-speech playback. EPUB 3 introduces three new technologies

to fill this void: PLS lexicon files enable producers to create reusable phonetic pro‐

nunciation libraries, SSML markup allows specific pronunciation overrides to be

embedded in the markup of a document, and the CSS3 Speech properties provide

a variety of playback controls. This chapter reviews how to include all these tech‐

nologies to improve the rendering on compliant reading systems.

Chapter 11: Validation

Before distributing your finished EPUB files, you want to make sure that they con‐

form to the specifications, otherwise you run the risk of them not being usable by

readers. The final chapter looks at the epubcheck validation program, including

how to run it and how to understand the errors it emits.

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