About DOCTYPE declaration

The DOCTYPE declaration tells the browser what version of HTML is being used.

This declaration must be the first thing in the document.

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

</head>
<body>

</body>
</html>

HTML 4.01 DTD - Document Type Definition

There are three document types for HTML 4.01 : Strict, Transitional, and Frameset.

Strict DTD: For strict documents

Deprecated elements and attributes, frames, and link's target are not allowed in Strict DTD.

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

URL not present
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">

Transitional DTD: For transitional documents

Deprecated elements and attributes, and link's target are allowed in Transitional DTD, but frames is not allowed.

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

URL not present
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

Frameset DTD: For documents that use frames

Frameset DTD is like Transitional DTD, but frames is allowed. Use this DTD for documents that use frames.

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

URL not present
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">

DOCTYPE switch

The DOCTYPE switch is used to switch rendering modes in the modern browsers.

There are the following two modes.

  • Standards mode : The strict rendering mode.
  • Quirks mode : The backwards compatible mode.
The rendering mode changes as follows
Doctype URL IE Firefox Opera
Strict present Standards Standards Standards
not present Standards Standards Standards
Transitional present Standards Standards Standards
not present Quirks Quirks Quirks