What Is XML

In the previous chapter you learned how HTML (HyperText Markup Language) uses tags to format data in a web page. Like HTML, Extensible Markup Language uses markup tags; however, its tags serve a different purpose — they are used to describe data content. HTML uses fixed, non-customizable tags to provide formatting instructions that should be applied to the data. XML is extensible, which means that it is not restricted to a set of predefined tags. XML allows you to invent your own tags in order to define and describe data stored in a wide range of documents. The XML parser does not care what tags you use; it only needs to be able to find the tags and confirm that the XML document is well formed. When a document is well formed, it follows the formatting rules for XML (see "What Is a Well-Formed XML Document?" below).

Part V

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