Preface

If you are a web designer or document author interested in sophisticated page styling, improved accessibility, and saving time and effort, this book is for you. All you really need before starting the book is a decent knowledge of HTML 4.0. The better you know HTML, of course, the better prepared you'll be. You will need to know very little else to follow this book.

This third edition of CSS: The Definitive Guide covers CSS2 and CSS2.1 (up through the 11 April 2006 Working Draft), the latter of which is, in many ways, a clarification of the first. While some CSS3 modules have reached Candidate Recommendation status as of this writing, I have chosen not to cover them in this edition (with the exception of some CSS3 selectors). I made this decision because implementation of these modules is still incomplete or nonexistent. I feel it's important to keep the book focused on currently supported and well-understood levels of CSS, and to leave any future capabilities for future editions.

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, variables in text, user-defined files and directories, commands, file extensions, filenames, directory or folder names, and UNC pathnames.

Constant width

Indicates command-line computer output, code examples, Registry keys, and keyboard accelerators.

Constant width bold

Indicates user input in examples.

Constant width italic

Indicates variables in examples and in Registry keys. It is also used to indicate variables or user-defined elements within italic text (such as pathnames or filenames). For instance, in the path \Windows\username, replace username with your name.

This icon signifies a tip, suggestion, or general note.

This icon indicates a warning or caution.

Property Conventions

Throughout this book, there are boxes that break down a given CSS property. These have been reproduced practically verbatim from the CSS specifications, but some explanation of the syntax is in order.

Throughout, the allowed values for each property are listed with the following syntax:

Value: [ <length> | thick | thin ]{1,4}

Value: [ <family-name> , ]* <family-name>

Value: <url>? <color> [ / <color> ]?

Value: <url> || <color>

Any words between "<" and ">" give a type of value or a reference to another property. For example, the property font will accept values that actually belong to the property font-family. This is denoted by the text <font-family>. Any words presented in constant width are keywords that must appear literally, without quotes. The forward slash (/) and the comma (,) must also be used literally.

Several keywords strung together means that all of them must occur in the given order. For example, help me means that the property must use those keywords in that exact order.

If a vertical bar separates alternatives (X | Y), then any one of them must occur. A vertical double bar (X || Y) means that X, Y, or both must occur, but they may appear in any order. Brackets ([...]) are for grouping things together. Juxtaposition is stronger than the double bar, and the double bar is stronger than the bar. Thus "V W | X || Y Z" is equivalent to "[ V W ] | [ X || [ Y Z ]]".

Every word or bracketed group may be followed by one of the following modifiers:

• An asterisk (*) indicates that the preceding value or bracketed group is repeated zero or more times. Thus, bucket* means that the word bucket can be used any number of times, including zero. There is no upper limit defined on the number of times it can be used.

• A plus (+) indicates that the preceding value or bracketed group is repeated one or more times. Thus, mop+ means that the word mop must be used at least once, and potentially many more times.

• A question mark (?) indicates that the preceding value or bracketed group is optional. For example, [pine tree]? means that the words pine tree need not be used (although they must appear in that exact order if they are used).

• A pair of numbers in curly braces ({M,N}) indicates that the preceding value or bracketed group is repeated at least M and at most N times. For example, ha{1,3} means that there can be one, two, or three instances of the word ha.

Some examples follow:

give || me || liberty

At least one of the three words must be used, and they can be used in any order. For example, give liberty, give me, liberty me give, and give me liberty are all valid.

[ I | am ]? the || walrus

Either the word I or am may be used, but not both, and use of either is optional. In addition, either the or walrus, or both, must follow in any order. Thus, you could construct I the walrus, am walrus the, am the, I walrus, walrus the, and so forth.

koo+ ka-choo

One or more instances of koo must be followed by ka-choo. Therefore, koo koo ka-choo, koo koo koo ka-choo, and koo ka-choo are all legal. The number of koos is potentially infinite, although there are bound to be implementation-specific limits.

I really{1,4}? [love | hate] [Microsoft | Netscape | Opera | Safari]

This is the all-purpose web designer's opinion expresser. This example can be interpreted as I love Netscape, I really love Microsoft, and similar expressions. Anywhere from zero to four reallys may be used. You also get to pick between love and hate, even though only love was shown in this example.

[[Alpha || Baker || Cray],]{2,3} and Delphi

This is a potentially long and complicated expression. One possible result would be Alpha, Cray, and Delphi. The comma is placed because of its position within the nested bracket groups.

Using Code Examples

This book is here to help you get your job done. In general, you may use the code in this book in your programs and documentation. You do not need to contact us for permission unless you're reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O'Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product's documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: "CSS: The Definitive Guide, Third Edition, by Eric A. Meyer. Copyright 2007 O'Reilly Media, Inc., 978-0-596-52733-4."

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [e-mail].

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Acknowledgments

I'd like to take a moment to thank the people who have backed me up during the long process of getting this book to its readers.

First, I'd like to thank everyone at O'Reilly for all they've done over the years, giving me my break into publishing and continuing to give me the opportunity to produce a book that matters. For this third edition, I'd like to thank Tatiana Apandi for her good humor, patience, and understanding as I played chicken with my deadlines.

I'd also like to thank most profoundly my technical reviewers. For the first edition, that was David Baron and Ian Hickson, with additional input from Bert Bos and Håkon Lie. The second edition was reviewed by Tantek Çelik and Ian Hickson. The fine folks who performed technical review on the third edition, the one you hold in your hands, were Darrell Austin, Liza Daly, and Neil Lee. All lent their considerable expertise and insight, keeping me honest and up-to-date on the latest changes in CSS as well as taking me to task for sloppy descriptions and muddled explanations. None of the editions, least of all this one, could have been as good as it is without their collective efforts, but of course whatever errors you find in the text are my fault, not theirs. That's kind of a cliché, I know, but it's true nonetheless.

Similarly, I'd like to thank everyone who pointed out errata that needed to be addressed. I may not have always been good about sending back email right away, but I read all of your questions and concerns and, when needed, made corrections. The continued feedback and constructive criticism will only help the book get better, as it always has.

There are a few personal acknowledgments to make as well.

To the staff of WRUW, 91.1 FM Cleveland, thank you for nine years of support, great music, and straight-out fun. Maybe one day I'll bring Big Band back to your airwaves, and maybe not; but either way, keep on keepin' on.

To Jeffrey Zeldman, thanks for being a great colleague and partner; and to the whole Zeldman family, thanks for being such wonderful friends.

To "Auntie" Molly, thanks for always being who you are.

To "Uncle" Jim, thanks for everything, both professionally and personally. It's no exaggeration to say I wouldn't be where I am without your influence, and our lives would be a good deal poorer without you around.

To the Bread and Soup CrewJim, Genevieve, Jim, Gini, Ferrett, Jen, Jenn, and Mollythanks for all your superb cooking and tasty conversation.

To my extended family, thank you as always for your love and support.

To anyone I should have thanked, but didn't: my apologies. And my thanks.

And to my wife and daughter, more thanks than I can ever express for making my days richer than I have any right to expect, and for showering me with more love than I could ever hope to repay. Though I'll keep trying, of course.

Cleveland Heights, Ohio

1 August 2006

Eric A. Meyer