18. The system of claim 11 , wherein the set of search results includes at least one content item.
11. A system for presenting results of a search customized using content preferences learned about a user, the system comprising: a non-transitory computer memory store comprising instructions in computer readable form that when executed cause a computer system to receive a user input action for interacting with an application on a user device; in response to receiving the user input action, send query information to a search engine, the query information including user information, the user information including (i) context information describing an environment in which the user input action was received, the context information adapted into a syntax understandable by the search engine, and (ii) a user signature representing content preferences learned about the user; generate customized search results by receiving a set of search results and auxiliary information from the search engine in response to sending the query information, the auxiliary information including information describing attributes of each search result of the set of search results that led to each search result being chosen by the search engine; order the set of search results based at least in part on the auxiliary information; and present, to the user, the ordered set of search results customized using the content preferences learned about the user.