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XHTML Introduction

XHTML is HTML written as XML

What Is XHTML?

  • XHTML stands for EXtensible HyperText Markup Language
  • XHTML is almost identical to HTML 4.01
  • XHTML is a stricter and cleaner version of HTML
  • XHTML is HTML defined as an XML application
  • XHTML is a W3C Recommendation of January 2000.
  • XHTML is supported by all major browsers.

Why XHTML?

Many pages on the internet contain "bad" HTML.

The following HTML code will work fine if you view it in a browser (even if it does NOT follow the HTML rules):

<html>
<head>
<title>This is bad HTML</title>
<body>
<h1>Bad HTML
<p>This is a paragraph
</body>

XML is a markup language where documents must be marked up correctly and "well-formed".

If you want to study XML, Read our XML tutorial.

Today's market consists of different browser technologies. Some browsers run on computers, and some browsers run on mobile phones or other small devices. Smaller devices often lack the resources or power to interpret a "bad" markup language.

Therefore - by combining the strengths of HTML and XML, XHTML was developed. XHTML is HTML redesigned as XML.

The Most Important Differences from HTML:

DOCUMENT STRUCTURE

  • XHTML DOCTYPE is mandatory
  • The XML namespace attribute in <html> is mandatory
  • <html>, <head>, <title>, and <body> is mandatory

ELEMENT SYNTAX

  • XHTML elements must be properly nested
  • XHTML elements must always be closed
  • XHTML elements must be in lowercase
  • XHTML documents must have one root element

ATTRIBUTE SYNTAX

  • XHTML attribute names must be in lower case
  • XHTML attribute values must be quoted
  • XHTML attribute minimization is forbidden

<!DOCTYPE ....> Is Mandatory

An XHTML document must have a XHTML DOCTYPE declaration.

A complete list of XHTML Doctypes is found in W3Schools' Tags Reference.

The <html, <head>, <title>, and <body> elements must also be present, and the xmlns attribute in <html>, must specify the xml namespace for the document.

The example below shows an XHTML document with a minimum of required tags:

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

<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<title>Title of document</title>
</head>

<body>
......
</body>

</html>

How to Convert from HTML to XHTML

  1. Add an XHTML <!DOCTYPE> to the first line of every page
  2. Add an xmlns attribute to the html element of every page
  3. Change all element names to lowercase
  4. Close all empty elements
  5. Change all attribute names to lowercase
  6. Quote all attribute values

Validate XHTML With The W3C Validator

Put your web address in the box below:

XHTML Quiz Test

The test contains 20 questions and there is no time limit.

The test is not official, it's just a nice way to see how much you know, or don't know, about XHTML.

You will get 1 point for each correct answer. At the end of the Quiz, your total score will be displayed. Maximum score is 20 points.

Start the XHTML Quiz

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