Feed::Parser::NS::Sy -- The RDF syndication module
Provides syndication hints to aggregators and others picking up this RDF Site Summary (RSS) feed regarding how often it is updated. For example, if you updated your file twice an hour, updatePeriod would be "hourly" and updateFrequency would be "2". The syndication module borrows from Ian Davis's Open Content Syndication (OCS) directory format. It supercedes the RSS 0.91 skipDay and skipHour elements.
Normally it would only be seen in RSS 1.0 (RDFSS) feeds. However like all RSS 1.0 modules, it sees use with both RSS 2.0 and Atom feeds.
xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
These were intended to be found in the RSS 1.0 "channel" element. They will also be processed if they're found in any other RSS "channel" element or in the Atom "feed" element.
Specified here: http://web.resource.org/rss/1.0/modules/syndication/