Cascading Style Sheets: The Definitive Guide

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 a syntax like the following:

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 which actually belong to the property font-family. This is denoted by using the text “<font-family>.” Any words presented in constant width text 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 would mean that the property must use those keywords in that exact order.

If a vertical bar ( X | Y ) separates alternatives, then any one of them must occur. A vertical double bar ( X || Y ) means that either X or 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 ...