<!DOCTYPE> specifies the HTML version of the page.
The browser needs this information to know how to interpret the HTML.
This declaration must appear on the first line of the document.
This <!DOCTYPE> specifies that the page uses HTML5.
<!DOCTYPE html>
doctype = document type
<!DOCTYPE> tells the browser which HTML version the page is using.
A web page must start with a <!DOCTYPE> declaration on the first line.
An outline of an HTML5 page, starting with !DOCTYPE.
<!DOCTYPE html>
<html>
<head>
<title>Page title goes here</title>
</head>
<body>
<!-- Page content goes here -->
</body>
</html>
Note: For HTML5 the DOCTYPE declaration is <!DOCTYPE html>.
Next are <!DOCTYPE> declarations for different HTML versions.
The older versions are rarely used, but browsers continue to support these.
!DOCTYPE for HTML5 is simple, because DTD (type definitions) has been withdrawn from HTML5.
<!DOCTYPE html>
This declaration includes all HTML elements and attributes, but not the deprecated ones, such as <font> and <plaintext>. Framesets are not allowed (framesets are panes that each load their own page)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
This declaration contains all HTML elements and attributes, including the deprecated ones, like <font>, <plaintext>, and <marquee>. Framesets are not allowed.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
This declaration is equal to HTML 4.01 Transitional, but it allows the use of framesets.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">
This declaration contains all HTML elements and attributes, without the ones that are deprecated, like <font> and <plaintext>. Framesets are not allowed. Markup must be well-formed XML.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
This declaration contains all HTML elements and attributes, including the deprecated ones, like <font> and <center>. Framesets are not allowed. Markup must be well-formed XML.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
This declaration is equal to XHTML 1.0 Transitional, but it allows the use of framesets.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
This declaration is equal to XHTML 1.0 Strict. It allows adding 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">
The <!DOCTYPE> tag is part of a group of tags that
define the structure of a web page.
This group is referred to as the Page tag group.
Together, they allow you to create solid, well-structured web pages.
Here is the complete list.
| Element | Description |
|---|---|
| <!DOCTYPE> | Must appear on the first line of a page. Specifies the HTML version |
| <html> | Defines the root container for an HTML document |
| <head> | Creates a head container that holds page-level metadata elements |
| <meta> | Provides metadata about a web page |
| <link> | Defines a link to an external source, such as a style sheet |
| <base> | Sets the base URL for all relative URLs on a page |
| <script> | Adds JavaScript to a page. Either client- or server-side |
| <style> | Adds CSS style elements to a page |
| <title> | Specifies the page title that displays in the browser's tab |
| <body> | Specifies a container for the content of the page, with text, links, images, etc. |
Here is when <!DOCTYPE> support started for each browser:
 Chrome
|
1.0 | Sep 2008 |
 Firefox
|
1.0 | Sep 2002 |
 IE/Edge
|
1.0 | Aug 1995 |
 Opera
|
1.0 | Jan 2006 |
 Safari
|
1.0 | Jan 2003 |
