According to HTML standards, each HTML document begins with a DOCTYPE declaration that specifies which version of HTML the document uses. Originally, the DOCTYPE declaration was used only by SGML-based tools like HTML validators, which needed to determine which version of HTML a document used (or claimed to use).
Today, many browsers use the document's DOCTYPE declaration to determine whether to use a stricter, more standards-oriented layout mode, or to use a "quirks" layout mode that attempts to emulate older, buggy browsers.
When we use the Java Script and CSS so that i declare the Doctype.
As a rule of thumb I use only Strict DOCTYPES, so:
HTML 4.01 Strict
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
XHTML 1.0 Strict
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
or more often used HTML 5:
Code:
<!DOCTYPE HTML>
Strict doctypes don't allow you to use presentational and deprecated tags such as <font> and frames. They force webmasters to use CSS for styling document.
<!DOCTYPE> element is meant to indicate the type of the current document - DTD (document type definition).
If you don't have it, the browser will not understand how to interprete a webpage correctly, because html exists in several versions.
What is a DOCTYPE? Which one do I use?
Linear Mode
