Throughout the book, we use a constant-width typeface to highlight any literal element of the HTML standard, and tags and attributes. We always use lowercase letters for HTML tags. (Although the language standard is case-insensitive with regard to tag and attribute names, this isn't so for other elements like source filenames, so be careful.) We use italic to indicate new concepts when they are defined and those elements you need to supply when creating your own documents, such as tag attributes or user-defined strings.
We discuss elements of the language throughout the book, but you'll find each one covered in depth (some might say nauseating detail) in a shorthand, quick-reference definition box that looks like the box on the following page.
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.
We use the following symbols to identify tags and attributes that are not in the HTML 3.2 standard (the last official version), but are additions to the language:
Netscape Navigator extension to the standard
Internet Explorer extension to the standard
The description also includes the ending tag, if any, for the tag, along with a general indication if the end tag may be safely omitted in general use.
"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 is a fairly "intertwined" language: 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. [the section called "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.