HTML DOCTYPE - Specifies the legal structure, elements and
attributes allowed in the html page.
A DOCTYPE binds a DTD (Document Type Definition) to the page
so that machine can understand what to expect in the document.
There are various formats of HTML documents like HTML 4.01
Transitional, HTML 4.01 Strict, and HTML 4.01 Frameset, etc. To tell machine
which document format to consider we use HTML DOCTYPE as very first line of the
HTML document. That also means no comments before the DOCTYPE declaration.
It is used in modern browsers for triggering appropriate
rendering mode so the page will render properly.
DOCTYPE is supported by all major browsers like IE, CHROME,
SAFARI, OPERA and FIREFOX.
Example - DOCTYPE for HTML 4 STRICT mode:
<!DOCTYPE HTML PUBLIC “-//W3c//DTD HTML 4.01 STRICT//EN”
href= “http://www.w3.org/TR/html4/strict.dtd”>
You might have noticed that there is no closing of DOCTYPE,
it is not required.
Now let’s see what information a HTML DOCTYPE declaration
holds in a page.
<!DOCTYPE - States DOCTYPE declaration goes here.
HTML - Type of Document (HTML default)
PUBLIC – Type of DTD publically available (Public/System)
“- - Tells whether if the organizations are registered for ISO
standards (+ for yes / - for no).
// - Is separator
W3C – Organization responsible for DTD creation and maintenance
(other is IETF)
//
DTD HTML 4.01 STRICT (DTD + Html
version + Format)
//
EN” - Language used for creation of reference object (DTD)
href= “http://www.w3.org/TR/html4/strict.dtd”
– Location of DTD file.
> end of DOCTYPE declaration.
Various formats of DOCTYPE are STRICT, TRANSITIONAL and
FRAMESET.
View list of various DOCTYPES at http://www.w3.org/QA/2002/04/valid-dtd-list.html
Sample HTML file with DOCTYPE
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 STRICT//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<!-- title tags
and meta tags here also include styles and script-->
</head>
<body>
<!-- all
information for your users here -->
</body>
</html>
Reference:
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