1. Introduction: Why XML Errors Break Systems Imagine you are trying to send a package, but you write the address in invisible ink or forget the zip code. The postal service cannot process it. It gets stuck, returned, or lost. XML (Extensible Markup Language) works the same way. It is the packaging language for data on the internet. It carries information between servers, databases, and applications. But unlike human readers who can guess what you meant if you make a typo, computers are incredibly strict. If you miss a single closing bracket > or misspell a tag, the entire system might reject your data. A website could crash, a data import could fail, or a configuration file could stop a game server from starting. This is where an XML Validator becomes essential. It is a diagnostic tool that scans your code to ensure it follows the strict rules of the XML standard. It doesn't just look for typos; it checks if your data structure is technically "legal" so computers can...