Applications commonly use XML documents to store and exchange data. XML defines rules for encoding documents in a format that is both human-readable and machine-readable. Chapter 1 introduces XML, tours the XML language features, and discusses well-formed and valid documents.
What Is XML?
XML (eXtensible Markup Language) is a meta-language (a language used to describe other languages) for defining vocabularies (custom markup languages), which is the key to XML’s importance and popularity. XML-based vocabularies (such as XHTML) let you describe documents in a meaningful way.
XML vocabulary documents are ...