Css: Understanding DOCTYPES and Effects on Browser Layout

by the3factory 2/29/2008 7:35:00 AM

HTML 4.01 has three document types: strict, transitional, and frameset. XHTML 1.1 has one document type, but XHTML 1.0 has three document types, like HTML 4.01. Only one document type definition (DTD) appears in the HTML document, using any one of the following:

HTML 4.01 Strict DTD:

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

HTML 4.01 Transitional DTD:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">

HTML 4.01 Frameset DTD:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
" http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd">

XHTML 1.0 Strict DTD:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

XHTML 1.0 Transitional DTD:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

XHTML 1.0 Frameset DTD:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

XHTML 1.1 DTD:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

Here's a basic page with the XHTML 1.1 DTD and the required head, body, and html tags.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html>
<head>
<title>XHTML DTD</title>
</head>
<body>
<p>XHTML requires having a DTD in every document otherwise it won't pass muster with the validators.</p>
</body>
</html>

DOCTYPE, short for DTD, defines an HTML or XHTML document's building blocks and tells the browsers and validators which version of HTML or XHTML your document is using.

The DOCTYPE declaration must appear at the beginning of every web page document before the html element to ensure your markup and CSS are standards compliant, and that browsers handle the pages based on the appropriate DTDs.

XHTML requires DOCTYPE, otherwise the pages won't validate and the browsers fall back on quirks mode, treating the pages as if they were written in invalid markup and therefore need to be improperly rendered in modern browsers even if the code may be perfect XHTML and CSS.

Tags: css