XML, XHTML and HTML are important markup languages used in web development and data structuring. While this is about the similarities they share, they serve different purposes and have unique characteristics. This article aims to highlight the differences between them, using explanations and code examples. **XML** XML (short for **eXtensible Markup Language**) is a markup language designed to store and transport data. XML focuses on describing the data structure and is both platform-independent and language-independent. Being platform-independent means that XML is a plain text format, which means that it can be created, edited, and processed on any platform or operating system without requiring specific software. Also, XML supports Unicode, enabling it to handle data in multiple languages and character sets universally. XML also uses a standardized syntax defined by the W3C, ensuring that the same XML file can be processed and understood on any platform with an XML parser. XML is said to be language-independent because it uses a tag-based format with a clear hierarchy, making it readable and understandable in any programming language. Most programming langauges (e.g. Python, Java, C#, etc) provide libraries or APIs to parse and process XML, enabling cross-language usage. XML focuses solely on data representation, not tied to any specific programming language or execution model. By adhering to these principles, XML ensures compatibility across diverse systems and software environments, making it a robust choice for data exchange. **Key Features of XML** 1. **Self-Descriptive:** XML documents are custom tags to define data, making it easy to understand. 2. **Flexible:** XML allows you to define your own tags based on the data requirements. 3. **Well-Formed:** An XML document must follow strict rules for syntax and structure. 4. **Extensible:** It provides no predefined tags, allowing customization for specific applications. **Example of XML** ``` <?xml version=”1.0” encoding=”UTF-8”?> <library> <book> <title>The Great Gatsby</title> <author>F. Scott Fitzgerald</author> <year>1949</year> </book> </library> ``` In this example, the custom tags **&lt;library&gt;, &lt;book&gt;, &lt;title&gt;, &lt;author&gt;, and &lt;year&gt;** define the structure of a library catalog. **XHTML** XHTML (short for **eXtensible HyperText Markup Language**) is a stricter and cleaner version of HTML. It combines the flexibility of XML with the functionality of HTML, ensuring that web documents adhere to rigorous standards. **Key Features of XHTML** 1. **XML Syntax:** XHTML documents must be well-formed and follow XML rules. 2. **Case Sensitivity:** Tags in XHTML must be in lowercase. 3. **Closing Tags:** All elements must be properly closed, including empty elements. 4. **Quotes Around Attributes:** Attribute values must be enclosed in quotes. 5. **Document Type Declaration:** XHMTL documents must declare their DOCTYPE. **Example of XHTML** ``` <!DOCTYPE html> <html xmlns=”http://www.w3.org/1999/xhtml”> <head> <title>My XHTML Page</title> </head> <body> <h1>Welcome to My XHTML Page</h1> <p>This is a paragraph of text.</p> <img src=”image.jpg” alt=”Sample Image” /> <a href=”https://example.com”>Visit Example</a> </body> </html> ``` This XHTML document is similar to what is obtainable with HTML but follows stricter syntax rules, such as lowercase tags and self-closing <img /> elements. **HTML** HTML (short for HyperText Markup Language) is the standard markup language for creating web pages. It is used to structure content on the web and is interpreted by web browsers to display text, images, and other multimedia elements. **Key Features of HTML** 1. **Predefined Tags:** HTML has a fixed set of tags such as &lt;p&gt;, &lt;h1&gt;, &lt;img&gt;, and &lt;a&gt;. 2. **Not Case-Sensitive:** Tags in HTML can be written in uppercase or lowercase. 3. **Not Strict Rules:** HTML is forgiving with syntax errors and can often still render a page even with mistakes. 4. **Focus on Presentation:** It is primarily used to define how content appears in a browser. **Example of HTML** ``` <!DOCTYPE html> <html> <head> <title>My Web Page</title> </head> <body> <h1>Welcome to My Web Page</h1> <p>This is a paragraph of text.</p> <img src=”image.jpg” alt=”Sample Image” /> <a href=”https://example.com”>Visit Example</a> </body> </html> ``` The HTML document creates a simple web page with a title, heading, paragraph, image and link. **When to use XML, XHTML, and HTML** **XML:** Use XML for data storage and exchange between systems, such as APIs or configuration files. **XHTML:** Use XHTML if you need stricter document validation or when working with applications that demand XML compliance. **HTML:** Use HTML for creating standard web pages that prioritize flexibility and broad browser support. In conclusion, XML, XHTML, and HTML are essential technologies with distinct purposes. While XML is for data storage and transport, HTML is for designing and structuring web pages, and XHTML combines the two having stricter rules for a cleaner structure. Understanding these differences will help you choose the appropriate language for your project and ensure effective communication between systems and browsers.