Info on XHTML

XHTML (Extensible Hyper Text Markup Language): Its extended, cleaner and sticker version of HTML, almost identical to HTML4.0. It is based on XML application, so one can say its a combination of HTML and XML.

Basic difference between HTML and XHTML are:

• XHTML elements must be properly nested.
• XHTML elements must always be closed.
• XHTML elements must be in lower case.
• XHTML documents must have one root element.

XHTML syntax rules are:

• Attribute names must be in lower case.
• Attribute values must be quoted.
• Attribute minimization is forbidden.
• The id attribute replaces the name attribute.
• The XHTML DTD defines mandatory elements :Doctype declaration, html,head and body tags are mandatory in XHTML documents.

Doctype specifies which DTD(Document type definition) is used by XHTML document. A DTD specifies the syntax of a web page in SGML. An XHTML DTD describes in precise, computer-readable language, the allowed syntax of XHTML markup.
There are 3 types of XHTML DTD

1. XHTML 1.1 Strict :for clean markup and free of presentational clutter. It declared as: !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
2. XHTML 1.1 Transitional : It is used when user want to use HTML presentational features. It declared as: !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
3. XHTML 1.1 Frameset : When HTML frames are used. It declared as: !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd"

After creating xhtml file and adding correct DTD, it can be validated using W3C Validator, using link http://www.w3schools.com/xhtml/default.asp