HTML Declaration

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HTML <!DOCTYPE> Declaration


Example
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>

<body>
The content of the document......
</body>

</html>



Definition and Usage
The <!DOCTYPE> declaration must be the very first thing in your HTML document, before the <html> tag.
The <!DOCTYPE> declaration is not an HTML tag; it is an instruction to the web browser about what version of HTML the page is written in.
In HTML 4.01, the <!DOCTYPE> declaration refers to a DTD, because HTML 4.01 was based on SGML. The DTD specifies the rules for the markup language, so that the browsers render the content correctly.
HTML5 is not based on SGML, and therefore does not require a reference to a DTD.
Tip: Always add the <!DOCTYPE> declaration to your HTML documents, so that the browser knows what type of document to expect.

Browser Support
Element





<!DOCTYPE>



chrome        edge           firefox                 safari          opera
Yes               Yes                  Yes                   Yes            Yes





Differences Between HTML 4.01 and HTML5
There are three different <!DOCTYPE> declarations in HTML 4.01. In HTML5 there is only one:
<!DOCTYPE html>





Tips and Notes
Tip: The <!DOCTYPE> declaration is NOT case sensitive.


Common DOCTYPE Declarations
HTML 5
<!DOCTYPE html>
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://will-power-forum.com/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://will-power-forum.com/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://will-power-forum.com/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://will-power-forum.com/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://will-power-forum.com/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://will-power-forum.com/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://will-power-forum.com/TR/xhtml11/DTD/xhtml11.dtd">
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