Starting with XHTML

Highly important rules to remember when writing XHTML code.

An XHTML page must have a DTD

A DocType Definition must be placed on the page above the opening html element. The most common DTD "transitional".

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

All code must be inside a single root element.

The page must be properly structured inside a single <html> element;

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

XHTML code must be written in lowercase.

No capital letters

<P>This is a Sentence</P> - Incorrect with the capital P elements


<p>This is a sentence</p> - Correct 
lowercase p elements

All code must be inside a tag (element).

This is a Sentence - Incorrect no p elements


<p>This is a sentence</p> - Correct open and closing p elements

All tags(elements) must be closed.

This includes images, non-breaking spaces and horizontal rules.

 <p>This is a Sentence - Incorrect no closing p element


<p>This is a sentence</p> - Correct open and closing p elements

All code must be properly nested.

Closed in the exact opposite of the opening.

<p><strong>This is a Sentence</p></strong> - Incorrect strong needs 
to be closed before the paragraph is closed


<p><strong>This is a sentence</strong></p> - Correct