VW support multiple input columns which are mapped to namespaces.
Note: when one wants to create quadratic features within VW you'd specify additionalFeatures.
Each feature column is treated as one namespace. Using -q 'uc' for columns 'user' and 'content'
you'd get all quadratics for features in user/content
(the first letter is called feature group and VW users are used to it... before somebody starts complaining ;)