XHTML Extensible hypertext markup language

XHTML (Extensible Hypertext Markup Language) is a markup language that follows the rules and syntax of XML (eXtensible Markup Language) while being designed to represent and structure web content in a way similar to HTML (Hypertext Markup Language). XHTML is a stricter and more structured version of HTML, and it combines the strengths of XML and HTML, making it more suitable for creating web pages that adhere to XML standards. Let's explore XHTML in detail:

1. XML-Based Markup Language: XHTML is based on XML, which means that it follows the strict syntax rules of XML. XML is a markup language that allows users to define their own tags, making it more flexible and extensible compared to HTML. XHTML documents are well-formed XML documents, meaning that they adhere to XML syntax rules, including proper nesting of elements and the use of opening and closing tags.
2. Compatibility with HTML: Although XHTML follows XML syntax rules, it is designed to be compatible with HTML, specifically the most widely used version at the time of XHTML's introduction, which was HTML 4.01. XHTML is meant to represent the same structure and content as HTML documents, but with the added benefits of XML's strictness and extensibility.
3. HTML Transitional and Strict: There are two main types of XHTML: XHTML Transitional and XHTML Strict. XHTML Transitional allows for a mix of HTML and XHTML elements, making it easier for developers to transition from HTML to XHTML. On the other hand, XHTML Strict is more rigid and does not permit any deprecated or non-standard HTML elements.
4. Well-Formed and Valid XHTML: To be considered well-formed, an XHTML document must adhere to XML syntax rules, such as proper nesting and the use of empty elements in self-closing form (e.g., <br />). In addition to being well-formed, a valid XHTML document must also adhere to the rules of a specified Document Type Definition (DTD) or XML Schema.
5. Application of Cascading Style Sheets (CSS): Like HTML, XHTML allows developers to apply Cascading Style Sheets (CSS) to control the presentation and layout of the web content. CSS separates the content from its presentation, allowing for more consistent and efficient website design.
6. Accessibility and Usability: XHTML promotes accessibility and usability by encouraging developers to create web content with clean and structured code. Properly structured documents are more accessible to users with disabilities, as they can be easily interpreted by assistive technologies like screen readers.
7. Semantic Web: XHTML contributes to the development of the Semantic Web by encouraging the use of meaningful and descriptive tags. Well-defined semantic elements help search engines and other applications better understand the content and context of web pages.
8. Browser Support: Most modern web browsers support both HTML and XHTML, allowing web developers to choose the markup language that best suits their needs and development practices.
9. XHTML5: With the introduction of HTML5, which is a revision of HTML rather than XHTML, the focus shifted back to HTML as the dominant markup language for web content. However, many of the principles and concepts of XHTML are still relevant and have been integrated into HTML5.

In summary, XHTML (Extensible Hypertext Markup Language) is a markup language that adheres to the syntax rules of XML while representing web content in a manner similar to HTML. XHTML combines the strengths of XML's strictness and extensibility with the familiarity of HTML's structure, making it suitable for creating well-formed and structured web pages. Although XHTML has been replaced by HTML5 as the dominant markup language for web content, the principles and concepts of XHTML continue to influence web development practices.