XML is a useful format for configuration, data storage, and transmitting data from one system to another. As a human readable format that can be easily read by machines it quickly gained favor in lots of different systems as a mechanism for data storage.
Many systems transparently make use of XML without the user ever seeing it. The API system SOAP is built around XML data, and it is normally possible to ask API endpoints to respond in either JSON or XML. It is common to see XML files used in configuration of systems as they can be easily edited and parsed when needed.
XML Schema Definitions (XSD) were first published by the W3C in 2001 and are one of a number of different XML schema formats that exist. Using this format we can look at a XML file and see straight away if it is valid or not and also provide some insight into why the XML is invalid. This prevents having to implement hard coded logic into your systems that attempt to validate the XML document.
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