15. A computer storage medium encoded with a computer program, the program comprising instructions that when executed by one or more computers cause the one or more computers to perform operations comprising: obtaining, by a search engine system, respective registration information from each of a plurality of publishers, the registration information including a location of respective enrichment information to be added to search results identifying resources provided by the respective publisher, each of the publishers being publishers registered with the search engine system; storing the registration information from the plurality of publishers for later use by the search engine system; receiving, by the search engine system, a query from a user; identifying, by the search engine system, a plurality of responsive resources, the plurality of responsive resources including a first responsive resource; determining, by the search engine system, that the first responsive resource is a resource for a first publisher that is associated with enrichment information; obtaining first enrichment information from the location of respective enrichment information included in the registration information provided by the first publisher to the search engine system; and providing, by the search engine system, in a response to the query, an enriched search result that identifies the first responsive resource and includes the first enrichment information.
15. A computer storage medium encoded with a computer program, the program comprising instructions that when executed by one or more computers cause the one or more computers to perform operations comprising: obtaining, by a search engine system, respective registration information from each of a plurality of publishers, the registration information including a location of respective enrichment information to be added to search results identifying resources provided by the respective publisher, each of the publishers being publishers registered with the search engine system; storing the registration information from the plurality of publishers for later use by the search engine system; receiving, by the search engine system, a query from a user; identifying, by the search engine system, a plurality of responsive resources, the plurality of responsive resources including a first responsive resource; determining, by the search engine system, that the first responsive resource is a resource for a first publisher that is associated with enrichment information; obtaining first enrichment information from the location of respective enrichment information included in the registration information provided by the first publisher to the search engine system; and providing, by the search engine system, in a response to the query, an enriched search result that identifies the first responsive resource and includes the first enrichment information. 18. The computer storage medium of claim 15 , wherein providing the enrichment information comprises obtaining the enrichment information from an enrichment information resource location distinct from a resource location for the first responsive resource.