XHTML » Tags » DOCTYPE

Syntax:
<!DOCTYPE ... >

The DOCTYPE tag is used to declare the DTD (Document Type Definition) for an XHTML document.

On a broader scale, XHTML, like HTML, is a subset of the SGML (Standardized Generalized Markup Language). SGML, and its various family members, use DTDs to define the context of the language. The W3C has defined a DTD to be:

    "...a collection of declarations that, as a collection, defines the legal
    structure, elements, and attributes that are available for use in a
    document that complies to the DTD."
Specifically, the XHTML DTD precisely defines the grammar, rules, and syntax that will apply to a document that has been created using XHTML. To repeat this in a different way, to be valid XHTML, the XHTML code that creates the XHTML document must obey all of the grammar, rules, and syntax in the XHTML DTD.
 
This tag is mandatory and must appear at the top (on the first line) of all XHTML code. If the DOCTYPE DTD tag is not present, then it is not XHTML code.
 
The exclamation mark (!) is required. This is the only tag in an XHTML document that is not closed. Obey the case and syntax.
 
Currently, there are three types of DTDs that apply to XHTML: Frameset, Strict, and Transitional. You must obey the syntax.
 
Frameset
 
This is declared when you have partitioned the HTML document into two or more frames (with or without using Cascading Style Sheets).
 
Syntax:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
 
Strict
 
This is declared when you use Cascading Style Sheets (CSS) to enhance the appearance and style of your HTML document. In general, you should only use this type of DTD if you are certain that your viewer has access to modern browsers that recognize CSS.
 
Syntax:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 
Transitional
 
This is declared when you are simply using HTML to create the appearance of the web page, rather than using Cascading Style Sheets (CSS). This type of DTD would ensure the widest viewing audience to your XHTML document.
 
Syntax:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

Examples

Code:
<!DOCTYPE html PUBLIC"-//W3C//DTD XHTML 1.0 Transitional/EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>DevGuru</title>
</head>
<body>
DevGuru is great!
<br />
</body>
</html>
Output:
DevGuru is great!
Explanation:

The basic XHTML document is composed of DOCTYPE, html, head, title, and body tags. Note that all tags in XHTML are closed except for the DOCTYPE.

Language(s): XHTML

Events

onclick

Syntax: onclick="action"

The onclick event is associated with the single click of a mouse on a selected HTML tag (element). Whenever you single click the element, the script code of the onclick is executed. This script can also call functions or subroutines which contain code that you want to run when the single click occurs.

ondblclick

Syntax: ondblclick="action"

The ondblclick event is associated with the double click of a mouse on a selected HTML element. Whenever you double click the element, the script code of the ondblclick is executed. This script can also call functions or subroutines which contain code that you want to run when the double click occurs.

onkeydown

Syntax: onkeydown="action"

The onkeydown event is associated with pressing down a key on the keyboard while the mouse is inside a selected HTML tag (element). In other words, the key down event occurred while the HTML element was in focus. Whenever you press down the key, the script code of the onkeydown is executed.

onkeypress

Syntax: onkeypress="action"

The onkeypress event is associated with press of a key on the keyboard while the mouse is inside a selected HTML element. In other words, the key press event occurred while the HTML element was in focus. Whenever you press the key, the script code of the onkeypress is executed.

onkeyup

Syntax: onkeyup="action"

The onkeyup event is associated with releasing up a key on the keyboard while the mouse is inside a selected HTML tag (element). In other words, the key up event occurred while the HTML element was in focus. Whenever you release the key, the script code of the onkeyup is executed.

onmousedown

Syntax: onmousedown="action"

The onmousedown event is associated with clicking down the mouse button while the mouse is inside a selected HTML tag (element). In other words, the mouse down event occurred while the HTML element was in focus. Every time you click down the mouse, while inside the element, the script code of the onmousedown is executed. This script can also call functions or subroutines which contain code that you want to run when this event occurs.

onmousemove

Syntax: onmousemove="action"

The onmousemove event is associated with moving the mouse around while inside a selected HTML tag (element). In other words, the mouse move event occurred while the HTML element was in focus. Every time you move the mouse around the element, the script code of the onmousemove is executed. This script can also call functions or subroutines that contain code that you want to run when this event occurs.

onmouseout

Syntax: onmouseout="action"

The onmouseout event is associated with moving the mouse out of a selected HTML tag (element). In other words, the mouse out event occurred while the HTML element was in focus. Every time you move the mouse out of the element, the script code of the onmouseout is executed. This script can also call functions or subroutines which contain code that you want to run when this event occurs.

onmouseover

Syntax: onmouseover="action"

The onmouseover event is associated with moving the mouse over a selected HTML tag (element). In other words, the mouse over event occurred while the HTML element was in focus. Every time you move the mouse over the element, the script code of the onmouseover is executed. This script can also call functions or subroutines which contain code that you want to run when this event occurs.

onmouseup

Syntax: onmouseup="action"

The onmouseup event is associated with the releasing up portion of a click of the mouse while inside a selected HTML tag (element). In other words, the mouse up event occurred while the HTML element was in focus. Every time you release the mouse up, while in the element, the script code of the onmouseup is executed. This script can also call functions or subroutines which contain code that you want to run when this event occurs.

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