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HTML vx. XHTML

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HTML and XHTML are two markup languages used to create webpages. While HTML has been the standard for decades, XHTML was introduced to enforce stricter rules and improve web standards compliance. Understanding the differences between HTML and XHTML is important for web developers to ensure proper coding practices, browser compatibility, and easier maintenance. In this chapter, you will learn what HTML and XHTML are, how they differ, how to write valid XHTML, and best practices for modern web development.

What Is HTML?

HTML (HyperText Markup Language) is the standard language for creating web pages. It uses tags to define elements such as headings, paragraphs, images, links, tables, and forms. HTML is flexible and forgiving, meaning browsers can usually display a page even if the code contains minor errors.

Example of Basic HTML

<!DOCTYPE html>
<html>
<head>
    <title>HTML Example</title>
</head>
<body>
    <h1>Welcome to HTML</h1>
    <p>This is a paragraph.</p>
    <img src="image.jpg" alt="Sample Image">
</body>
</html>

Here, the browser can render the page even if minor mistakes exist, such as missing closing tags.

What Is XHTML?

XHTML (eXtensible HyperText Markup Language) is a stricter version of HTML. It combines HTML with XML rules, making the code more structured and precise. XHTML enforces stricter syntax, which helps browsers parse content more consistently.

Key Features of XHTML

  • All tags must be properly closed.

  • Tag names are always in lowercase.

  • Attribute values must be quoted.

  • Documents must be well-formed.

  • Nested elements must be correctly structured.

Example of XHTML

<!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>XHTML Example</title>
</head>
<body>
    <h1>Welcome to XHTML</h1>
    <p>This is a paragraph.</p>
    <img src="image.jpg" alt="Sample Image" />
</body>
</html>

Notice that the <img> tag is self-closed with /, and all elements and attributes follow strict rules.

Differences Between HTML and XHTML

Feature HTML XHTML
Syntax Flexible, browsers are forgiving Strict, must follow XML rules
Tag Closing Optional for some tags All tags must be closed properly
Case Sensitivity Tag names can be uppercase or lowercase Tag names must be lowercase
Attribute Quotes Optional in some cases Required
Document Type   Specific XHTML DTD (Strict, Transitional, Frameset)
Error Handling Browsers try to correct errors Browsers may not render incorrectly formed code
Parsing HTML parser XML parser

Why XHTML Was Introduced

XHTML was created to:

  • Improve consistency across browsers

  • Make web pages compatible with XML tools

  • Encourage better coding practices

  • Prepare web content for new technologies like mobile devices and XML-based systems

By enforcing stricter rules, XHTML made it easier for automated tools and search engines to parse content accurately.

Writing Valid XHTML

To write valid XHTML, follow these rules:

  1. Always use lowercase tag names.

    <p>Paragraph</p> <!-- Correct -->
<P>Paragraph</P> <!-- Incorrect -->

  2. Close all tags properly.

    <br /> <!-- Correct -->
<br>   <!-- Incorrect -->

  3. Quote all attribute values.

    <img src="image.jpg" alt="Sample" /> <!-- Correct -->
<img src=image.jpg alt=Sample>      <!-- Incorrect -->

  4. Nest elements correctly.

    <p><strong>Bold Text</strong></p> <!-- Correct -->
<p><strong>Bold Text</p></strong> <!-- Incorrect -->

  5. Include a proper DOCTYPE.

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

Modern Use of HTML vs XHTML

With HTML5, the web has shifted back to simpler, flexible markup. HTML5 allows:

  • Cleaner syntax

  • Built-in support for multimedia

  • Less strict rules while maintaining browser compatibility

XHTML is rarely used for new projects, but understanding it helps in:

  • Maintaining legacy websites

  • Using XML-based systems

  • Ensuring web standards compliance in strict environments

Example: HTML vs XHTML

HTML Version

<p>This is a paragraph with <strong>bold</strong> text.</p>
<img src="image.jpg" alt="Image">

XHTML Version

<p>This is a paragraph with <strong>bold</strong> text.</p>
<img src="image.jpg" alt="Image" />

Notice the self-closing <img /> tag in XHTML.

Summary of HTML vx. XHTML

HTML is flexible and widely used for creating web pages, allowing browsers to correct small mistakes. XHTML is a stricter variant that combines HTML with XML rules, enforcing proper tag closure, lowercase tags, and quoted attributes. While HTML5 has largely replaced XHTML for modern websites, understanding XHTML helps maintain legacy sites, ensures proper syntax, and prepares you for XML-compatible applications. For new projects, HTML5 is preferred due to simplicity, compatibility, and ease of use.

Practice Questions

Q1. Write a simple HTML document using lenient syntax.

Q2. Convert an HTML document into valid XHTML format.

Q3. Demonstrate the use of self-closing tags in XHTML.

Q4. Show how attribute values differ in HTML and XHTML.

Q5. Explain why XHTML requires case sensitivity.

Q6. Write a form in XHTML with properly quoted attributes.

Q7. Validate an XHTML file using a W3C validator.

Q8. Identify and correct syntax errors in a mixed HTML/XHTML page.

Q9. Compare error handling in HTML vs. XHTML.

Q10. Explain why XHTML is more compatible with XML tools.

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