HTML The Definitive Guide (24 page)

Chapter 3

Anatomy of an HTML

Document

3.5 HTML Document Elements

Every HTML document should conform to the HTML SGML DTD, the formal Document Type Definition that defines the HTML standard. The DTD defines the tags and syntax that are used to create an HTML document. You can inform the browser which DTD your document complies with by placing a special SGML (Standard Generalized Markup Language) command in the first line of the document:

This cryptic message indicates that your document is intended to be compliant with the HTML 4.0

final DTD defined by the World Wide Web Consortium (W3C). Other versions of the DTD define more restricted versions of the HTML standard, and not all browsers support all versions of the HTML DTD. In fact, specifying any other doctype may cause the browser to misinterpret your document when displaying it for the user. It's also unclear what doctype to use when including in the HTML document the various tags that are not standards, but are very popular features of a popular browser - the Netscape extensions, for instance, or even the deprecated HTML 3.0 standard, for which a DTD was never released.

Almost no one precedes their HTML documents with the SGML doctype command. Because of the confusion of versions and standards, we don't recommend that you include the prefix with your HTML documents either.

3.5.1 The Tag

As we saw earlier, the and tags serve to delimit the beginning and end of an HTML document. Since the typical browser can easily infer from the enclosed source that it is an HTML document, you don't really need to include the tag in your source document.

Function:

Delimits a complete HTML document

Attributes:

DIRLANGVERSION

End tag:

; may be omitted

Contains:

head_tag
,
body_tag, frames

That said, it's considered good form to include this tag so that other tools, particularly more mundane text-processing ones, can recognize your document as an HTML document. At the very least, the presence of the beginning and ending tags ensures that the beginning or the end of the document haven't been inadvertently deleted.

Inside the tag and its end tag are the document's head and body. Within the head, you'll find tags that identify the document and define its place within a document collection. Within the body is the actual document content, defined by tags that determine the layout and appearance of the document text. As you might expect, the document head is contained within a tag and the body is within a tag, both of which are defined later.

The tag may be replaced by a tag, defining one or more display frames that,
in turn, contain actual document content. See Chapter 12, Frames
, for more information.

By far, the most common form of the tag is simply:

document head and body content

When the tag appears without the version attribute, the HTML document server and browser assume the version of HTML used in this document is supplied to the browser by the server.

3.5.1.1 The dir attribute

The dir attribute specifies in which direction the browser should render text within the containing element. When used within the tag, it determines how text will be presented within the entire document. When used within another tag, it controls the text's direction for just the content of that tag.

By default, the value of this tag is ltr, indicating that text is presented to the user left-to-right. Use the other value, rtl, to display text right-to left for languages like Chinese or Hebrew.

3.5.1.2 The lang attribute

When included within the tag, the lang attribute specifies the language you've generally used within the document. When used within other tags, the lang attribute specifies the language you used within that tag's content. Ideally, the browser will use lang to better render the text for the user.

Set the value of the lang attribute to an ISO-639 standard two-character language code. You may also indicate a dialect by following the ISO language code with a dash and a subcode name. For example, "en" is the ISO language code for English; "en-US" is the complete code for US English.

Other common language codes include "fr" (French), "de" (German), "it" (Italian), "nl" (Dutch), "el"

(Greek), "es" (Spanish), "pt" (Portuguese), "ar" (Arabic), "he" (Hebrew), "ru" (Russian), "zh"

(Chinese), "ja" (Japanese), and "hi" (Hindu).

3.5.1.3 The version attribute

The version attribute defines the HTML standard version used to compose the document. Its value should read exactly:

version="-//W3C//DTD HTML 4.0//EN"

In general, version information within the tag is more trouble than it is worth, and this attribute has been deprecated in HTML 4.0. Serious authors should instead use an SGML

tag at the beginning of their documents, like this:

"http://www.w3c.org/TR/REC-html40/strict.dtd"> 3.4 Document Content

3.6 The Document Header