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The idea behind Writing XHTM is CLEAN HTML syntax.
Attribute Names Must Be In Lower Case
This is wrong:
<table WIDTH="100%">
This is correct:
<table width="100%">
Attribute Values Must Be Quoted
This is wrong:
<table width=100%>
This is correct:
<table width="100%">
Attribute Minimization Is Forbidden
This is wrong:
<input checked>
<input readonly>
<input disabled>
<option selected>
<frame noresize>
This is correct:
<input checked="checked" />
<input readonly="readonly" />
<input disabled="disabled" />
<option selected="selected" />
<frame noresize="noresize" />
The id Attribute Replaces The name Attribute
HTML 4.01 defines a name attribute for the elements a, applet, frame, iframe, img, and map. In XHTML the name attribute is deprecated. Use id instead.
This is wrong:
<img src="picture.gif" name="picture1" />
This is correct:
<img src="picture.gif" id="picture1" />
Note: To interoperate with older browsers for a while, you should use both name and id, with identical attribute values, like this:
<img src="picture.gif" id="picture1" name="picture1" />
The Lang Attribute
The lang attribute applies to almost every XHTML element. It specifies the language of the content within an element.
If you use the lang attribute in an element, you must add the xml:lang attribute, like this:
<div lang="no" xml:lang="no">Heia Norge!</div>
Mandatory XHTML Elements
All XHTML documents must have a DOCTYPE declaration. The html, head and body elements must be present, and the title must be present inside the head element.
This is a minimum XHTML document template:
<!DOCTYPE Doctype goes here>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Title goes here</title>
</head><body>
Body text goes here
</body></html>
Note: The DOCTYPE declaration is not a part of the XHTML document itself. It is not an XHTML element, and it should not have a closing tag.
Note: The xmlns attribute inside the <html> tag is required in XHTML. However, the validator on w3.org does not complain when this attribute is missing in an XHTML document. This is because "xmlns=http://www.w3.org/1999/xhtml" is a fixed value and will be added to the <html> tag even if you do not include it.
The XHTML standard defines three Document Type Definitions.
The most common is the XHTML Transitional.
The <!DOCTYPE> Is Mandatory
An XHTML document consists of three main parts:
the DOCTYPE
the Head
the Body
The basic document structure is:
<!DOCTYPE ...>
<html>
<head>
<title>... </title>
</head>
<body> ... </body>
</html>
The DOCTYPE declaration should always be the first line in an XHTML document.
An XHTML Example
This is a simple (minimal) XHTML document:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>simple document</title>
</head>
<body>
<p>a simple paragraph</p>
</body>
</html>
The DOCTYPE declaration defines the document type:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
The rest of the document looks like HTML:
<html>
<head>
<title>simple document</title>
</head>
<body>
<p>a simple paragraph</p>
</body>
</html>
The 3 Document Type Definitions
DTD specifies the syntax of a web page in SGML.
DTD is used by SGML applications, such as HTML, to specify rules that apply to the markup of documents of a particular type, including a set of element and entity declarations.
XHTML is specified in an SGML document type definition or 'DTD'.
An XHTML DTD describes in precise, computer-readable language, the allowed syntax and grammar of XHTML markup.
There are currently 3 XHTML document types:
STRICT
TRANSITIONAL
FRAMESET
XHTML 1.0 specifies three XML document types that correspond to three DTDs: Strict, Transitional, and Frameset.
XHTML 1.0 Strict
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
Use this when you want really clean markup, free of presentational clutter. Use this together with Cascading Style Sheets.
XHTML 1.0 Transitional
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Use this when you need to take advantage of HTML's presentational features and when you want to support browsers that don't understand Cascading Style Sheets.
XHTML 1.0 Frameset
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
Use this when you want to use HTML Frames to partition the browser window into two or more frames.
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