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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 almost identical to HTML
  • XHTML is stricter than HTML
  • XHTML is HTML defined as an XML application
  • XHTML is supported by all major browsers

Why XHTML?

Many pages on the internet contain "bad" HTML. This HTML code works fine in most browsers (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 an markup language where everything has to be marked up correctly, which results in "well-formed" documents.

XHTML was developed to make HTML more extensible and flexible to work with other data formats (such as XML).

The Most Important Differences

  • <!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
XHTML Example
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