1.1. What Are RSS and Atom for?
The original, and still the most common, use for RSS and Atom is to provide a content syndication feed: a consistent, machine-readable file that allows web sites to share their content with other applications in a standard way. Originally, as shown in the next section, this was used to share data among web sites, but now it's most commonly used between a site and a desktop application called a reader.
Feeds can be anything from just headlines and links to stories to the entire content of the site, stripped of its layout and with metadata liberally applied. Content syndication allows users to experience a site on multiple devices and be notified of updates over a variety of services. It can range from a simple list of links sent from site to site to the beginnings of the Semantic Web.
However, feeds are starting to be used as content in their own right: people are building services that only output to a feed and don't actually have a "real" site at all. In later chapters of this book, we'll look at the cool things you can do with this, and build some of our own.