The source namespace is a collection of add-ons to RSS 2.0 that provide information about where the content in the feed comes from, so it's possible that aggregators can provide a richer experience for readers. It's the format that Fargo generates starting in version 1.64.
Example feeds
The feed for my blog, Scripting News, implements some of the features outlined here.
Others are implemented in the feed for my linkblog.
source:account
A channel-level element.
Has one required attribute, service, the name of a service such as "twitter" or "facebook". The value is case insensitive, so Twitter is the same as twitter.
<source:account service="facebook">dave.winer.12</source:account>
The value of source:account is the username or screenname of the author of the feed on the indicated service.
source:outline
An item-level element.
Exactly the same as the OPML outline element.
In RSS, it contains the source of the outline used to render the text of the item.
Useful if the aggregator has the ability to render outlines on its own.
<source:outline text="A silly example" created="Sun, 13 Jul 2014 12:54:20 GMT" type="idea" >
The example above is very simple and contains no nested structure, which is what makes outlines useful. Check out the Scripting News feed for more extensive examples.
source:archive
A channel-level element.
Links to the calendar-structured archive for the feed.
The folder pointed to by this address contains one folder for each year, 2009, 2010, 2011, etc.
Each of those folders contains one folder for each month, 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12. The month folders must be zero-padded to two places. Folders may be missing, indicating that there is no archived content for the month.
Each of the month folders contains folders for the days of the month. Day folder names are also zero-padded to two places and may be missing if there were no updates on the given day.
Each day folder contains a file named rss.xml, unless the optional <source:filename> sub-element is supplied, which overrides the default. This makes it possible for a single calendar structure to store the archive of more than one feed.
<source:archive> must contain at least two sub-elements: <source:link>, the address of the archive and <source:startDay>, a hyphen-delimited date, formatted as yyyy-mm-dd, for the first element of the archive.
It may contain two optional sub-elements: <source:endDay> which is the hyphen-delimited date (yyyy-mm-dd) for the last element in the archive; and <source:filename> as expained above.
If <source:endDay> defaults to the pubDate of the feed, if it's specified. If not, it defaults to the current date.
<source:archive>
<source:url>http://static.scripting.com/myReallySimple/</source:url>
<source:filename>linkblog.xml</source:filename>
<source:startDay>2010-12-25</source:startDay>
<source:endDay>2014-07-14</source:endDay>
</source:archive>
source:localTime
An item-level element.
<source:localTime>3/15/2011; 10:34:54 AM</source:localTime>
A simple entirely human-readable way for the editor of the site to see what time, in his or her time zone, the feed was last updated. Must-have for debugging and sanity-preservation if you have trouble converting GMT to local time in your head (as I do). The format here is entirely up to the editor of the site.
source:linkFull
An item-level element.
It's the unshortened version of <link>.
<source:linkFull>http://nyu.edu/stories/very-long-name/</source:linkFull>
Only include this elemement when <link> is a shortened url.