What is a .xml file?

You opened a file full of angle brackets and nested tags. That's XML — a format designed to structure data in a way that's both human-readable and machine-parseable. Every piece of data gets an opening tag and a closing tag, which makes XML verbose but unambiguous.

XML was supposed to be the universal language of the internet. That vision was partly realised and partly replaced by JSON, which is less verbose and easier to work with for web APIs. But XML never went away — it powers RSS feeds, SOAP web services, SVG graphics, Android layouts, Maven build configurations, and the internals of every DOCX, XLSX, and PPTX file (unzip one and look inside). Enterprise software runs on XML. Configuration files use XML. It's not trendy, but it's everywhere.

Any text editor opens XML. VS Code provides syntax highlighting, formatting, and schema validation. Your browser renders XML in a navigable tree view. For transforming or querying XML, XPath and XSLT are the standard tools. XML is the technology you'll encounter whether you seek it out or not.