HTML versus XHTML

XHTML stands for EXtensible HyperText Markup Language. It is a stricter, more XML-based version of HTML.

XHTML is HTML defined as an XML application.

XHTML is supported by all major browsers

XHTML was developed to make HTML more extensible and flexible to work with other data formats (such as XML). Besides, browsers ignore errors in HTML pages, and try to display the website even if it has some errors in the markup. Not so with XHTML.

The Most Important Differences from HTML

<!DOCTYPE> is mandatory
The xmlns attribute in <html> is mandatory
<html>, <head>, <title>, and <body> are mandatory
Elements must always be properly nested
Elements must always be closed
Elements must always be in lowercase
Attribute names must always be in lowercase
Attribute values must always be quoted
Attribute minimization is forbidden

An Example

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

  some content here...

</body>
</html>

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