XML (eXtensible Markup Language) is a notation system designed to describe data. XML has become a standard for describing and transferring data over the Internet.
In this lesson you will learn to recognize XML by seeing how Popfly blocks use XML to describe their inputs, outputs, and operations. Next, you will examine data from an RSS feed to view its underlying XML, and build a Popfly mashup to display it. Finally, you will learn a little bit about web services, and examine the XML that is generated when a Popfly block calls a web service.
Under the Covers: A Beginner’s Guide to Learning about XML using Popfly (PDF)