XML
XML (Extensible Markup Language) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. It is widely used for representing structured data, facilitating data interchange between different systems, and storing configuration information. XML documents consist of elements defined by tags, attributes, and text content, with a hierarchical tree structure.
Developers should learn XML for scenarios involving data interchange, configuration files, and web services, as it provides a standardized way to structure data across platforms. It is essential in legacy systems, SOAP-based web services, and document formats like Microsoft Office files, where interoperability and validation through schemas (e.g., XSD) are critical. However, for modern web APIs, JSON is often preferred due to its lighter weight and better integration with JavaScript.