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In computing, an HTML element indicates structure in an HTML document and a way of hierarchically arranging content. More specifically, an HTML element is an SGML element that meets the requirements of one or more of the HTML Document Type Definitions (DTDs). These elements have properties: both attributes and content, as specified (both allowable and required) according to the appropriate HTML DTD (for example, the HTML 4.01 strict DTD). Elements may represent headings, paragraphs, hypertext links, lists, embedded media, and a variety of other structures.

Syntactically HTML elements are constructed with:

• a start tag marking the beginning of an element
• any number of attributes (and their associated values)
• some amount of content (characters and other elements)
• an end tag (note: Empty elements should not have an end tag. It is optional for some others.)

Many HTML elements include attributes in their start tags, defining desired behavior or indicating additional element properties. The end tag is optional for many elements; in a minimal case, an empty element has no content and requires no end tag. There are a few elements that are not part of any official DTDs, yet are supported by some browsers and used by some web pages. Such elements may be ignored or displayed improperly on browsers not supporting them.

Informally, HTML elements are sometimes referred to as "tags" (an example of synecdoche), though many prefer the term tag strictly in reference to the semantic structures delimiting the start and end of an element.

XHTML is the successor to HTML 4.01; XHTML 1.0 supports the same elements as HTML 4 and in most cases valid XHTML 1.0 documents will be valid or nearly valid HTML 4 documents. XHTML 1.0 migrates HTML from its SGML underpinnings to an XML foundation. Accordingly, the discussion of elements within this article focuses on the final SGML based HTML, version 4.01 (unless noted otherwise). However, to the extent that XHTML 1.0 elements remain identical to the HTML 4.01 elements, the discussion remains applicable (see HTML for a discussion of the minor differences in content between XHTML 1.0 and HTML 4.01).

[edit] Head elements

<title>…</title>

Define a document title. This element is required in every HTML and XHTML document. Different user agents may make use of the title in different ways. For example:

• Web browsers usually display it in a window's title bar when the window is open, and in the task bar when the window is minimized.

• It may become the default filename when saving the page.

• Search engines' Web crawlers may pay particular attention to the words used in the title.

The title element must not contain any nested tags (that is, it cannot contain any other elements). Only one title element is permitted in a document.

<base>

Specifies a base URL for all relative href and other links in the document. Must appear before any element that refers to an external resource. HTML permits only one base element for each document. The base element has attributes, but no contents.

<link>

Specifies links to other documents, such as "previous" and "next" links, or alternate versions [1]. A common use is to link to external stylesheets, using the form

<link rel="stylesheet" type="text/css" href="url" title="description_of_style">[2]

A less-common, but important, usage is to supply navigation hints consistently through use of microformats. Several common relationships are defined, that may be exposed to users through the browser interface rather than directly in the web page.

<link rel="next" href="url">

A document's head element may contain any number of link elements. The link element has attributes, but no contents.

<basefont> (deprecated)

Specifies a base font size, typeface, and color for the document. Used together with font elements. Deprecated in favor of stylesheets.

<script>…</script>

Used to add JavaScript or other scripts to the document. The script code may be typed literally between the script tags or may be given in a separate resource whose URL is specified with the script element's optional src attribute. [3]

<style>…</style>

Specifies a style for the document, usually in the form

<style type="text/css">…</style>

The CSS (Cascading Style Sheets) statements may be typed literally between the style tags or may be given in separate resources whose URLs are specified with @import directives of the form

<style> @import url; </style>. [4]

<object>…</object>

Used for including generic objects within the document header. Though rarely used within a head element, it could potentially be used to extract foreign data and associate it with the current document.

<meta>

Can be used to specify additional metadata about a document, such as its author, publication date, expiration date, page description, keywords, or other information not provided through the other header elements and attributes. Because of their generic nature, meta elements specify associative key-value pairs.

In one form, meta elements can specify

[edit] References

1. ^ "Description of the BLACKFACE tag". Retrieved on 2008-07-31.

[edit] See also

• Microformat - use of abbr and attributes

[edit] External links

• Complete lists of elements and attributes for HTML 4.01

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