HTML: Basic Tags

<!DOCTYPE...>

Identifies the kind of document that this is; browsers can display different kinds of documents according to different rules, based on what the possible doctypes are. The Doctype also includes a reference to the standard definition, so the browser can, if it needs, get the definitions of the doctype, and draw your document accordingly.

HTML 3.2 Final The HTML 3.2 specification is now out of date.
HTML 4.01 Strict In HTML 4.01 Strict, your document is expected to comply absolutely with the HTML 4.01 standard; because this can be difficult,
HTML 4.01 Transitional will give you a little latitude for sloppiness; similarly,
HTML 4.01 Frameset will give you the benefits of Transitional, plus the additional Frameset tags, which are not part of the Strict HTML specification.
XHTML 1.0 Strict HTML is essentially dead; further developments will fall under the XHTML rubric, which is similar, but ultimately quite different. XHTML 1.0 Strict will require your documents to adhere to the absolute definition of XHTML.
XHTML 1.0 Transitional will give you a little leeway, as with HTML 4.01 Transitional, to work out some quirks and residual old HTML.
XHTML 1.0 Frameset as Transitional, but with Framesets.
XHTML 1.1 Strict only, this is the hardest standard to match, but is inevitable.

Example

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/html4/loose.dtd">

This is probably the safest Doctype to use right now. For a document that sets up a frameset, use:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
        "http://www.w3.org/TR/html4/frameset.dtd">

For more on Doctypes, see A List Apart.

HTML Tutorials

HTML: Basic Tags

<!DOCTYPE...>

Example

HTML Tutorials

Basics

Content & Structure: HTML

Form: CSS

Action: JavaScript