By asking her RSS reader to subscribe to the URL of an RSS feed, a user instructs the application to begin fetch- ing that URL at regular intervals. When it is retrieved, its XML payload is interpreted as a list of RSS items by the application. Items may be composed of just a head- line, an article summary, or a complete story in HTML; each entry must have a unique ID, and is frequently ac- companied by a permanent URL (“permalink”) to a Web version of that entry. To the user, each item typically appears in a chronologically-sorted list; in this way, RSS client applications have become, for many users,.
