RSS was originally created in 1999 by Netscape as a channel description framework for their My Netscape Network. MNN was a portal system that allowed end users to selectively view new content from their choice of content providers. RSS was created as a means of gathering that content. Since its creation, RSS has been updated and expanded to handle a much wider range of content with a far broader range of uses.
Simple Web Syndication with RSS 2.0 - Expanding your content listing (Page 5 of 6 )
Now we’ll take a moment to list the additional sub-elements that relate to your channel items. The elements provide extra information specific to each piece of content offered.
Element
Description
author
The email address of the content author.
category
Adds a category for your item.
comments
The URL of a page containing comments, such as blog or forum, relating to the item.
enclosure
Describes the media attached to an item.
guid
A unique string used to identify your item.
pubDate
The publication date of the item
source
The RSS channel that the item came from.
Here I’ve added some additional elements to my channel item.
<item>
<title>A New Toolbar Can Boost Your Web Site Traffic Dramatically</title>
I’ve used the comment sub-element to provide the URL for the article discussion blog. For the guid I just used the URL of the article since it’s always unique. Not setting item guids can prevent news readers from updating your listing properly. The pubDate has been set to show when the article went live on DevArticles.com.
XML 
Introduction to RSS
