When working with the repository query API, it's not possible at this time (or very bothersome) to query a list of contents matching some criteria and limiting the query to a subtree of the sitemap (for example retrieve all the contents which are referenced by any page under a certain section).
It would be interesting to have the possibility to do that, for instance with a subclass of ContentQuery with a 'page' or 'path' parameter on the execute method.