As per this thread Help tracking page properties it doesn’t appear that there is any native way to track a piece of content with multiple ‘topics’ or ‘properties’.
For example, I’d like to record against a pageview that a particular piece of content is about Piwik, but also about Google. Or has two authors, Same and Jodie.
The best I can come up with given current functionality is this:
_paq.push([‘trackContentImpression’, ‘topic’, ‘piwik’, ‘’]);
_paq.push([‘trackContentImpression’, ‘topic’, ‘google’, ‘’]);