XHTML

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XHTML

"The Extensible Hypertext Markup Language, or XHTML, is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax."

In other words: XHTML is a stricter and cleaner version of HTML.

The Document

An XHTML document consists of three main parts:

the DOCTYPE
the Head
the Body

DOCTYPE DTD

XHTML Strict DTD

<!DOCTYPE html PUBLIC 
  "-//W3C//DTD XHTML 1.0 Strict//EN" 
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

XHTML Transitional DTD

<!DOCTYPE html PUBLIC 
   "-//W3C//DTD XHTML 1.0 Transitional//EN" 
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

XHTML Frameset (Transitional) DTD

<!DOCTYPE html PUBLIC 
  "-//W3C//DTD XHTML 1.0 Frameset//EN" 
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

Notes:

This tag tells the browser which HTML or XHTML specification the document uses.
The <!DOCTYPE> tag does not have an end tag.

Links

W3Schools: Learn XHTML

Wikipedia: XHTML

"The Extensible Hypertext Markup Language, or XHTML, is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax...."

XHTML Validator