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HTML vs XHTML

What is XHTML?

XHTML (Extensible HyperText Markup Language) is a stricter, more XML-based version of HTML. It was designed to bridge the gap between HTML and XML. While HTML5 has become the standard, understanding the differences between HTML and XHTML is important for maintaining legacy code and understanding web standards evolution.

Key Differences

Here are the main differences between HTML and XHTML:

1. DOCTYPE Declaration

HTML5: Simple DOCTYPE declaration:

Example - HTML5

<!DOCTYPE html>

XHTML: More complex DOCTYPE declaration:

Example - XHTML

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

2. Document Structure

HTML5: Simple html tag:

Example - HTML5

<html lang="en">

XHTML: Requires xmlns attribute:

Example - XHTML

<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">

3. Element Naming

HTML5: Case-insensitive element names (though lowercase is recommended):

Example - HTML5 (Valid)

<div>Content</div>
<DIV>Content</DIV>  <!-- Valid but not recommended -->

XHTML: Case-sensitive, must be lowercase:

Example - XHTML

<div>Content</div>  <!-- Valid -->
<DIV>Content</DIV>  <!-- Invalid -->

4. Closing Tags

HTML5: Some elements can be self-closing or not closed:

Example - HTML5 (Valid)

<img src="image.jpg" alt="Description">
<br>
<hr>

XHTML: All elements must be properly closed:

Example - XHTML

<img src="image.jpg" alt="Description" />
<br />
<hr />

5. Attribute Quoting

HTML5: Attribute values can be unquoted in some cases (though quoting is recommended):

Example - HTML5 (Valid but not recommended)

<div class=container id=main>Content</div>

XHTML: All attribute values must be quoted:

Example - XHTML

<div class="container" id="main">Content</div>

6. Attribute Minimization

HTML5: Boolean attributes can be minimized:

Example - HTML5 (Valid)

<input type="checkbox" checked>
<input type="checkbox" checked="checked">  <!-- Also valid -->

XHTML: Boolean attributes must have values:

Example - XHTML

<input type="checkbox" checked="checked" />
<input type="checkbox" disabled="disabled" />

7. Nesting

HTML5: More forgiving with nesting errors:

Example - HTML5 (Tolerated)

<p>Text <strong>Bold</p></strong>  <!-- Tolerated but incorrect -->

XHTML: Strict nesting rules:

Example - XHTML

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

Comparison Table

Feature	HTML5	XHTML
DOCTYPE	Simple: `<!DOCTYPE html>`	Complex DTD declaration
Element Names	Case-insensitive (lowercase recommended)	Case-sensitive (must be lowercase)
Closing Tags	Optional for some elements	Required for all elements
Attribute Values	Quoting optional (recommended)	Must be quoted
Boolean Attributes	Can be minimized	Must have values
Nesting	More forgiving	Strict rules
Error Handling	More forgiving (error recovery)	Strict (fails on errors)
MIME Type	`text/html`	`application/xhtml+xml`

Complete Example Comparison

HTML5 Example

Example - HTML5

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>My Page</title>
</head>
<body>
    <img src="image.jpg" alt="Description">
    <br>
    <p>Text <strong>Bold</strong></p>
</body>
</html>

XHTML Example

Example - XHTML

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>My Page</title>
</head>
<body>
    <img src="image.jpg" alt="Description" />
    <br />
    <p>Text <strong>Bold</strong></p>
</body>
</html>

When to Use HTML5 vs XHTML

Use HTML5 (Recommended)

Modern web development: HTML5 is the current standard
Better browser support: Better support in modern browsers
Simpler syntax: Easier to write and maintain
New features: Includes new semantic elements, APIs, and features
Widely adopted: Most websites use HTML5

Use XHTML (Legacy)

Legacy systems: When maintaining older XHTML code
XML compatibility: When XML tools are required
Strict validation: When strict validation is required
Enterprise systems: Some enterprise systems may require XHTML

Best Practices

Use HTML5: HTML5 is the recommended standard for modern web development
Follow HTML5 conventions: Use lowercase, quote attributes, close tags properly
Write valid code: Validate your HTML code regularly
Be aware of differences: Understand differences when working with legacy code
Consider XHTML when needed: Use XHTML only when specifically required

Converting HTML to XHTML

To convert HTML to XHTML, follow these rules:

Change DOCTYPE to XHTML DTD
Add xmlns attribute to html tag
Make all element names lowercase
Close all elements properly
Quote all attribute values
Add values to all boolean attributes
Ensure proper nesting
Change MIME type to application/xhtml+xml

Conclusion

HTML5 is the current standard and recommended for all new web development. XHTML was an important step in web standards evolution, but HTML5 has largely replaced it. Understanding the differences is valuable for maintaining legacy code and understanding web standards history, but for new projects, HTML5 is the clear choice.

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