DOCTYPES

<!DOCTYPES ...>

XHTML DTDs :

The <!DOCTYPE ...> declaration is MANDANTORY in xhtml and ALWAYS the first line.

There are three XHTML DTDs:

* STRICT
* TRANSITIONAL
* FRAMESET

Thier declarations are as follows:

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 the strict DOCTYPE when you want really clean markup, free of presentational clutter. Use it together with CSS.

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 the transitional DOCTYPE when you want to still use HTML's presentational features.

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 the frameset DOCTYPE when you want to use HTML frames.

Other xhtml notes:

When using any of the xhtml doctypes I found that to pass validation I had to also:

declare an xml namespace with an xmlns= statement to the html tag
specify character type

eg:

<html xmlns='http://www.w3.org/1999/xhtml' lang='en-US' xml:lang='en-US'>
  <head>
    <title>blah</title>
    <meta  http-equiv='Content-Type' content='text/html; charset=iso-8859-1' />
  </head>
...

You can validate your web pages here: http://validator.w3.org


Here are more doctypes that I have not had time to html-ify for this 
page which basically came from here:

  http://www.w3schools.com/tags/tag_doctype.asp


HTML 4.01 Strict

This DTD contains all HTML elements and attributes, but does NOT INCLUDE 
presentational or deprecated elements (like font). 
Framesets are not allowed.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 
    "http://www.w3.org/TR/html4/strict.dtd">


HTML 4.01 Transitional

This DTD contains all HTML elements and attributes, INCLUDING presentational 
and deprecated elements (like font). 
Framesets are not allowed.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
    "http://www.w3.org/TR/html4/loose.dtd">


HTML 4.01 Frameset

This DTD is equal to HTML 4.01 Transitional, but allows the use of 
frameset content.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" 
    "http://www.w3.org/TR/html4/frameset.dtd">


XHTML 1.0 Strict

This DTD contains all HTML elements and attributes, but does NOT INCLUDE 
presentational or deprecated elements (like font). 
Framesets are not allowed. 
The markup must also be written as well-formed XML.

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


XHTML 1.0 Transitional

This DTD contains all HTML elements and attributes, INCLUDING 
presentational and deprecated elements (like font). 
Framesets are not allowed. 
The markup must also be written as well-formed XML.

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


XHTML 1.0 Frameset

This DTD is equal to XHTML 1.0 Transitional, but allows the use of 
frameset content.

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


XHTML 1.1

This DTD is equal to XHTML 1.0 Strict, but allows you to add modules (for 
example to provide ruby support for East-Asian languages).

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" 
    "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">