Text Conventions (HTML & XHTML: The Definitive Guide, 4th Edition)

0.2. Text Conventions

Throughout the book, we use a constant-width typeface to highlight any literal element of the HTML/XHTML standards, tags, and attributes. We always use lowercase letters for tags.[1] We use italic to indicate new concepts when they are defined and for those elements you need to supply when creating your own documents, such as tag attributes or user-defined strings.

[1]HTML is case-insensitive with regard to tag and attribute names, but XHTML is case-sensitive. And some HTML items like source filenames, are case-sensitive, so be careful.

We discuss elements of the language throughout the book, but you'll find each one covered in depth (some might say in nauseating detail) in a shorthand, quick-reference definition box that looks like the following box. The first line of the box contains the element name, followed by a brief description of its function. Next, we list the various attributes, if any, of the element: those things that you may or must specify as part of the element.

<html>

Function:

Delimits a complete HTML document

Attributes:

DIR

VERSION

LANG

End tag:

</html>; may be omitted in HTML

Contains:

head_tag, body_tag, frames

We use the following symbols to identify tags and attributes that are not in the HTML 4.01 or XHTML 1.0 standards, but are additions to the languages:

Netscape Navigator extension to the standards

Internet Explorer extension to the standards

The description also includes the ending tag, if any, for the element, along with a general indication whether or not the end tag may be safely omitted in general use with HTML. With the few tags that do not have an end tag in HTML, but for which XHTML requires one, the language lets you indicate that ending with a forward slash (/) at the end of the tag, such as <br />. In these cases, the tag also may contain attributes, indicated with an intervening elipsis, such as <br ... />.

"Contains" names the rule in the HTML grammar that defines the elements to be placed within this tag. Similarly, "Used in" lists those rules that allow this tag as part of their content. These rules are defined in Appendix A, "HTML Grammar".

Finally, HTML and XHTML are fairly intertwined languages. You will occasionally use elements in different ways depending on context, and many elements share identical attributes. Wherever possible, we place a cross-reference in the text that leads you to a related discussion elsewhere in the book. These cross-references, like the one at the end of this paragraph, serve as a crude paper model of hypertext documentation, one that would be replaced with a true hypertext link should this book be delivered in an electronic format. Section 3.3.1, "The Syntax of a Tag"

We encourage you to follow these references whenever possible. Often, we'll only cover an attribute briefly and expect you to jump to the cross-reference for a more detailed discussion. In other cases, following the link will take you to alternative uses of the element under discussion or to style and usage suggestions that relate to the current element.