<!DOCTYPE> tag

HTML <!DOCTYPE> Tag

<!DOCTYPE> defines the document type declaration(DTD).

You must place this in the first line of html document just before the <html> tag. In short, this should be the first statement in the HTML document.

This simply informs the browser about the version of the HTML or XHTML document. There is no content inside this tag and there is no closing tag also.

The <!DOCTYPE> declaration is not case-sensitive but it is better to write it in uppercase.

Most Preferred Syntax:
<!DOCTYPE html>
This is the most used syntax for this declaration. Other types are also listed in the page below.

DOCTYPE Declarations

The HTML 4.01 indicates the <!DOCTYPE> declaration for DTD but you do not require to refer DTD for HTML5.

Overall, you can divide the declarations based on the HTML and XHTML versions –

HTML 5
HTML 4.01 Strict
HTML 4.01 Transitional
HTML 4.01 Frameset
XHTML 1.01 Strict
XHTML 1.01 Transitional
XHTML 1.01 Frameset
XHTML 1.1

HTML5

This is the most common declaration. Most of the website designers prefers this declaration. You must have only one declaration in the entire document like below –

<!DOCTYPE html>

HTML 4.01 Strict

This includes all the elements and attributes but does not include the deprecated elements and the elements which comes with the framesets.

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

HTML 4.01 Transitional

It includes all the elements and attributes. This also includes the deprecated elements but this does not allow framesets.

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

HTML 4.01 Frameset

It includes all the elements and attributes including the deprecated elements. This also allows framesets.

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

XHTML 1.01 Strict

It contains a strict layout of a markup. It includes all the elements and attributes but does not include the deprecated elements. This does not allow framesets.

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

XHTML 1.01 Transitional

It contains a strict layout of a markup. It includes all the elements(including deprecated elements) and attributes. This does not allow framesets.

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

XHTML 1.01 Frameset

It contains a strict layout of a markup. It includes all the elements and attributes including the deprecated elements. This also allows framesets.

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

XHTML 1.1

It contains a strict layout of a markup. It includes all the elements and attributes but does not include the deprecated elements. This does not allow framesets while you can add different modules.

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

Example

<!DOCTYPE html>
<html>
<body>
 <h2>Example of HTML DOCTYPE declaration</h2>
 <p>Welcome to TutorialBrain</p>
 <p>DOCTYPE must be the first line in the HTML document <p>
</body>
</html>

How Browser will display

NONE

Difference between HTML4.01, XHTML and HTML5

HTML4	XHTML	HTML5
HTML4 has different versions as HTML 4.01 strict, HTML 4.01 transitional & HTML 4.01 frameset. Each of these has its own DOCTYPE declarations	XHTML has their declaration as XHTML 1.01 strict, XHTML 1.01 transitional, XHTML 1.01 frameset and XHTML 1.1. Each of these has its own DOCTYPE declarations	It has only one DOCTYPE declaration for the entier document

Attributes used