What is XML?

Extensible markup language (XML) is a flexible type of markup language that was designed to structure, store or transport data. In many ways, XML is more than a markup language: XML actually provides a framework for defining markup languages.

Since it was officially recommended by the World Wide Web Consortium (W3C) in 1998, the XML syntax has been used to develop several XML-based formats, including really simple syndication (RSS), simple object access protocol (SOAP) and extensible hypertext markup language (XHTML).

A markup language is a system for annotating documents and content. Perhaps the best known markup language is the hypertext markup language (HTML), which introduced the World Wide Web. However, whereas HTML was designed to “display” content, XML was designed to transport and store data – though it can also contribute to what is displayed. In fact, Microsoft Office, Apple’s iWork, OpenOffice.org and other office productivity tools now use XML-based formatting.

Comparing XML and HTML

One way to understand XML is by comparing it to HTML:

Purpose Display content and data Transport/store content and data
Tags Uses predefined tags Has NO predefined tags
Closing tags Preferred but not strict Mandatory
Case Insensitive to case Sensitive to case
White space Not preserved Preserves white space
Processing Viewable with all browsers Needs a processing application
Readable By humans By humans and machines/programs


It’s important to understand that XML was not designed to replace HTML. If anything, XML has become a popular supplement to XML.

For example, this website is powered by WordPress, a content management system (CMS) that produces HTML web pages for visitors. However, WordPress uses XML for much of its data and content storage.

XML is a valuable tool for web developers and digital marketers, especially in today’s data-driven world.


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