<http://schema.org/description>
"Piwik offers a plugin architecture, that allows you to build plugins without modifying the Piwik core. This article will give an introduction to the Piwik plugin architecture and show you how to build your own plugin.  What can a plugin..."^^<http://www.w3.org/2001/XMLSchema#string>
<http://geekmonkey.org/2012/10/how-to-write-a-piwik-plugin/>