HTML vs. XHTML

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

What is XHTML?

• XHTML stands for EXtensible HyperText Markup Language

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

• XHTML is HTML defined as an XML application

• XHTML is supported by all major browsers

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.

If you want to study XML, please read our XML Tutorial.

The Most Important Differences from HTML

• is mandatory

• The xmlns attribute in is mandatory

• , , , and 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

XHTML - 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 namespace for the document.

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>

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:

Wrong:

XHTML Empty Elements Must Always be Closed

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

Correct:

Wrong:

XHTML Elements Must be in Lowercase

In XHTML, element names must always be in lowercase, like this:

Correct:

Wrong:

XHTML Attribute Names Must be in Lowercase

In XHTML, attribute names must always be in lowercase, like this:

Correct:

<a href=" our HTML tutorial</a>

Wrong:

<a HREF=" our HTML tutorial</a>

XHTML Attribute Values Must be Quoted

In XHTML, attribute values must always be quoted, like this:

Correct:

<a href=" our HTML tutorial</a>

Wrong:

<a href= our HTML tutorial</a>

XHTML Attribute Minimization is Forbidden

In XHTML, attribute minimization is forbidden:

Correct:

Wrong:

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