Description #
XHTML (Extensible Hypertext Markup Language) is a stricter, XML-based version of HTML that enforces well-formed syntax and compatibility with XML parsers, making it more consistent and predictable than classic HTML.
History #
XHTML was standardized by the W3C in 2000 as a successor to HTML 4.01. It was created to merge the flexibility of HTML with the rigor of XML, but later gave way to HTML5, which relaxed many of its strict rules.
Hello World Code #
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Hello XHTML</title>
</head>
<body>
<h1>Hello, World!</h1>
</body>
</html>How to Run #
Option 1: Online
Use a W3C XHTML validator or paste into a browser with .xhtml extension:
https://validator.w3.org/
Option 2: Local
Save the above as hello.xhtml and open in a browser.
Ensure it is served with the MIME type application/xhtml+xml for full compliance.
Key Concepts #
- Based on XML; all tags must be properly closed
- Attributes must be quoted and lowercase
- Case-sensitive tag names and attributes
- Enforces well-formedness
- Compatible with XML tools and parsers
- Backward-compatible with most HTML browsers
- Must use a valid DOCTYPE
- Commonly used in academic, publishing, and standards-heavy environments
- Can be styled with CSS or scripted with JavaScript like HTML
- Declined in favor of HTML5 but still supported
Try It Online #
https://validator.w3.org/
(Paste in XHTML to validate or preview)
Fun Facts #
- XHTML was once required by the U.S. federal government for accessible web apps.
- It was part of the XHTML 1.0, 1.1, and Modularization series—but XHTML2 was later abandoned.
- XHTML documents must be served with the correct MIME type, or they behave like regular HTML.
Resources #
Official site
Docs or tutorial
GitHub or interpreter
Community or learning resources
