Developing Feeds with RSS and Atom

Introducing Modules

Modules are additional sets of elements, giving the feed a greater range of expression: they allow the specification to be extended without actually being changed, which is a very clever trick. You can make your own module match any data you might wish to syndicate. Admittedly, most aggregators will ignore it, but your own applications can take advantage of it. And, happily, the most popular modules are increasingly being supported by the latest aggregators as a matter of course.

Modules in RSS, both Versions 2.0 and 1.0, are created with a system known as XML Namespaces. Namespaces are the XML solution to the classic language problem of one word meaning two things in different contexts. Take “Windows,” for example. In the context of houses, “windows” are holes in the wall through which we can look. In the context of computers, “Windows” is a trademark of the Microsoft Corporation and refers to its range of operating systems. The context within which the name has a particular meaning is called its namespace.

In XML, you can distinguish between the two meanings by assigning a namespace and placing the namespace’s name in front of the element name, separated by a colon, like this:

<computing:windows>This is an operating system</computing:windows>

<building:windows>This is a hole in a wall</building:windows>

Namespaces solve two problems. First, they allow you to distinguish between different meanings for words that are spelled the same way, which means you can use ...