HTML Versus XHTML

Date: 11-21-24

XHTML is a stricter, more XML-based version of HTML.

What is XHTML?

Why XHTML?

XML is a markup language where all documents must be marked up correctly (be "well-formed"). XHTML was developed to make HTML more extensible and flexible to work with other data formats (such as XML). In addition, browsers ignore errors in HTML pages, and try to display the website even if it has some errors in the markup. So XHTML comes with a much stricter error handling.

The Most Important Differences from HTML

XHTML - <!DOCTYPE....> Is Mandatory

An XHTML document must have an XHTML <!DOCTYPE> declaration. The <html>, <head>, <title>, and <body> elements must also be present, and the xmlns attribute in <html> must specify the xml namesspace for the document.

Example

Here is an XHTML document with a minimum of required tags:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="https://www/w3/org/1999/xhtml">
<head>
<title>Title of document</title>
</head>
<body>

some content here...

</body>
</html>

XHTML Elements Must be Properly Nested

In XHTML, elements must always be properly nested within each other, like this:

Correct:

<b><i>Some text</i></b>

Wrong:

<b><i>Some text </b></i>

XHTML Elements Must Always be Closed

In XHTML, elements must always be closed, like this:

Correct:

<a href="https://www.w3schools.com/html">Visit our HTML tutorial</a>

Wrong

<a href=https://www.w3schools.com/html/>Visit our HTML tutorail</a>

XHTML Attribute Minimization is Forbidden

In XHTML, attribute minimization is forbidden:

Correct:

<input type="checkbox" name="vehicle" value"car" checked="checked" />
< input type="text" name="lastname" disabled="disabled" />

Wrong:

<input type="checkbox" name="vehicle" value="car" checked />
<input type="tex" name="lastname" disabled />