What is XML eXtended Markup Language
XHTML: Extensible HyperText Markup Language
XHTML (Extensible HyperText Markup Language) is a reformulation of HTML (HyperText Markup Language) as an application of XML (Extensible Markup Language). It combines the structural advantages of XML with the content focus of HTML.
Key Characteristics of XHTML
- XML-based: XHTML documents are XML documents, adhering strictly to XML syntax rules. This includes case sensitivity, proper nesting of elements, and mandatory closing tags.
- HTML Compatibility: XHTML is designed to be compatible with HTML 4.01, allowing for gradual migration.
- Extensibility: Like XML, XHTML allows for the creation of custom elements and attributes, providing flexibility for developers.
- Stricter Syntax: Compared to HTML, XHTML has stricter syntax rules, leading to more well-formed and valid documents.
- Validation: XHTML documents can be validated using standard XML validators, ensuring correctness and compatibility.
Structure of an XHTML Document
An XHTML document consists of:
- Document Type Declaration (DTD): Specifies the document type and references the appropriate DTD or XML schema.
- Root Element: The top-level element of the document, typically
<html>. - Elements: Represent different parts of the document, such as headings, paragraphs, links, images, etc.
- Attributes: Provide additional information about elements.
- Text Content: The actual content of the document.
Advantages of XHTML
- Improved Structure: XHTML's XML-based structure enhances document organization and maintainability.
- Better Interoperability: XHTML documents can be processed by a wider range of applications due to their XML compliance.
- Validation: Strict syntax rules allow for easier error detection and correction.
- Extensibility: Developers can create custom elements and attributes to suit specific needs.
Disadvantages of XHTML
- Steeper Learning Curve: XHTML's stricter syntax can be more challenging for developers accustomed to HTML's relaxed rules.
- Browser Compatibility: While most modern browsers support XHTML, older browsers might have issues.
- Limited Adoption: XHTML hasn't gained as widespread adoption as HTML, due to the challenges mentioned above.
XHTML vs. HTML
| Feature | HTML | XHTML |
|---|---|---|
| Syntax | Relaxed, case-insensitive, optional closing tags | Strict XML syntax, case-sensitive, required closing tags |
| Validation | Lenient, browser-specific | Strict, XML-based validation |
| Extensibility | Limited | Enhanced through custom elements and attributes |
Conclusion
XHTML offers a more structured and extensible approach to web development compared to HTML. While it didn't achieve widespread dominance, it has influenced the evolution of web standards and continues to be relevant in certain contexts.