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The following is both a reference and a practical example of the application of
XHTML to a web page. To view the code for this page, select "view source" from your browser menue.
XHTML — EXtensible HyperText Markup Language
XHTML is essentially HTML, but with a more strict application and a few syntax
differences. Recommended by the W3C in 2000, it is a preferred version of HTML specifically for
use with XML applications. The following describes how XHTML is different from HTML:
- Must be well-formed.
Most browsers interpret poorly formed HTML which has created a proliferance of "breaking the rules". Code MUST be compliant:
- Elements must be properly nested: <b><i>text</i></b>
- All tags properly closed
- Must have one root element: <html></html>
- All attribute values enclosed in quotes.
- Syntax should be in lowercase.
- Tags without a closing tag should include a space and "/" to close the tag: <br />
- Tags with un-quoted attributes should be quoted - example:
<input checked> should be <input checked=”checked” />
- The "id" attribute replaces the "name" attribute. Both "id" and "name" may be used for compatibility with older browsers.
DOCTYPE declaration
Must have a DOCTYPE declaration - Note: The DOCTYPE declaration is not a part of the XHTML and should not have a closing tag. Should always be the first line. Example:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Untitled Document</title>
</head>
<body>
</body>
</html>
There are three XHTML DTDs (declared in DOCTYPE):
- STRICT – when you want really clean markup, free of presentational clutter. Use together with CSS.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
- TRANSITIONAL - when you want to still use HTML's presentational features
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
- FRAMESET – use with framesets (obviously)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
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>
XHTML Modules
W3C has split the definition of XHTML into 28 modules:
| Module Name |
Description |
| Applet Module |
Defines the deprecated* applet element |
| Base Module |
Defines the base element |
| Basic Forms Module |
Defines the basic forms elements |
| Basic Tables Module |
Defines the basic table elements |
| Bi-directional Text Module |
Defines the bdo element |
| Client Image Map Module |
Defines browser side image map elements |
| Edit Module |
Defines the editing elements del and ins |
| Forms Module |
Defines all elements used in forms |
| Frames Module |
Defines the frameset elements |
| Hypertext Module |
Defines the a element |
| Iframe Module |
Defines the iframe element |
| Image Module |
Defines the img element |
| Intrinsic Events Module |
Defines event attributes like onblur and onchange |
| Legacy Module |
Defines deprecated* elements and attributes |
| Link Module |
Defines the link element |
| List Module |
Defines the list elements ol, li, ul, dd, dt, and dl |
| Metainformation Module |
Defines the meta element |
| Name Identification Module |
Defines the deprecated* name attribute |
| Object Module |
Defines the object and param elements |
| Presentation Module |
Defines presentation elements like b and i |
| Scripting Module |
Defines the script and noscript elements |
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| Server Image Map Module |
Defines server side image map elements |
| Structure Module |
Defines the elements html, head, title and body |
| Style Attribute Module |
Defines the style attribute |
| Style Sheet Module |
Defines the style element |
| Tables Module |
Defines the elements used in tables |
| Target Module |
Defines the target attribute |
| Text Module |
Defines text container elements like p and h1 |
* Deprecated elements should not be used in XHTML.
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