XHTML (Extensible Hypertext Markup Language) is a variant of HTML (Hypertext Markup Language) that is based on XML (Extensible Markup Language). XHTML combines the flexibility of HTML with the strictness and structure of XML. Here are some key aspects and features of XHTML:
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Structure and Syntax:
- Well-formedness: XHTML documents must be well-formed, meaning they must adhere to all XML rules. This includes correctly nested and closed tags.
- Elements and Attributes: All elements and attributes in XHTML must be written in lowercase.
- Closing Tags: All tags must be closed, either with a corresponding end tag (e.g.,
<p></p>) or as self-closing tags (e.g., <img />).
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Compatibility:
- XHTML is designed to be backward compatible with HTML. Many web browsers can render XHTML documents even if they were initially developed for HTML documents.
- XHTML documents are treated as XML documents, meaning they can be parsed by XML parsers. This facilitates the integration of XHTML with other XML-based technologies.
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Doctype Declaration:
- An XHTML document begins with a doctype declaration that specifies the document type and the version of XHTML being used. For example:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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Practical Use:
- XHTML was developed to address the shortcomings of HTML and provide a stricter structure that improves document interoperability and processing.
- Although XHTML offers many advantages, it has not been fully adopted. HTML5, the latest version of HTML, incorporates many of XHTML's benefits while maintaining the flexibility and ease of use of HTML.
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Different XHTML Profiles:
- XHTML 1.0: The first version of XHTML, offering three different DTDs (Document Type Definitions): Strict, Transitional, and Frameset.
- XHTML 1.1: An advanced version of XHTML that provides a more modular structure and better support for international applications.
- XHTML Basic: A simplified version of XHTML specifically designed for mobile devices and other limited environments.
In summary, XHTML is a stricter and more structured variant of HTML based on XML, offering advantages in certain application areas. It was developed to improve web interoperability and standardization but has not been fully adopted due to the advent of HTML5.
