21. The system of claim 14 , wherein the answer box precursor includes code for obtaining content from a publisher server for the first publisher.
14. A system comprising one or more computers configured to perform operations comprising: receiving a query; receiving a plurality of search results responsive to the query, each search result identifying a resource responsive to the query; after receiving the plurality of search results responsive to the query, accessing an index of resources to determine, for a plurality of the identified resources, that each identified resource is associated with a respective answer box topic; determining a set of answer box topics from the respective answer box topics; analyzing each answer box topic of the set of answer box topics to identify a first answer box topic that is responsive to the query, the first answer box topic associated with a first search result of the plurality of search results; identifying a first publisher of a first resource identified by the first search result; obtaining an answer box precursor for the first answer box topic using a mapping between a plurality of answer box topics and a plurality of answer box precursors, wherein the mapping includes mapping information provided by the first publisher of the first resource; and providing the search results along with the answer box precursor for the first answer box topic, wherein the answer box precursor includes information that defines an answer box.