13. A method comprising: providing an interface for providing or identifying content for custom search engines; receiving via the interface, for each of a plurality of custom search engines, either initial content to be searched or identification of initial content to be searched for each custom search engine; creating an index in association with a first custom search engine of the plurality of custom search engines in response to receiving an identifier of initial content for the first custom search engine in the interface; receiving via the interface, for each of the plurality of custom search engines, identification of additional content to be searched for each of the respective custom search engines; receiving a search query at a first electronic device from a requestor electronic device; receiving an identification from the requestor electronic device that identifies the first custom search engine of the plurality of custom search engines; searching the initial content for the first custom search engine based on the search query and the index to produce initial search results that include a plurality of items; generating sub-queries for respective ones of the items in the plurality of items in the initial search results, the generating sub-queries is based on rules for the first custom search engine, wherein the rules for the first custom search engine specify a field in each of the plurality of items in the initial search results, and the generating a sub-query includes generating the sub-queries based on information in the fields of the respective items; obtaining additional search results that match the sub-queries, including searching the additional content for the first custom search engine; generating a search result set from the initial search results and the additional search results, the generating a search result set is based on the rules for the first custom search engine and includes augmenting respective ones of the items in the initial search results with an additional search result obtained from the sub-query for the respective item in the initial search results; and providing the search result set to the requestor electronic device.
13. A method comprising: providing an interface for providing or identifying content for custom search engines; receiving via the interface, for each of a plurality of custom search engines, either initial content to be searched or identification of initial content to be searched for each custom search engine; creating an index in association with a first custom search engine of the plurality of custom search engines in response to receiving an identifier of initial content for the first custom search engine in the interface; receiving via the interface, for each of the plurality of custom search engines, identification of additional content to be searched for each of the respective custom search engines; receiving a search query at a first electronic device from a requestor electronic device; receiving an identification from the requestor electronic device that identifies the first custom search engine of the plurality of custom search engines; searching the initial content for the first custom search engine based on the search query and the index to produce initial search results that include a plurality of items; generating sub-queries for respective ones of the items in the plurality of items in the initial search results, the generating sub-queries is based on rules for the first custom search engine, wherein the rules for the first custom search engine specify a field in each of the plurality of items in the initial search results, and the generating a sub-query includes generating the sub-queries based on information in the fields of the respective items; obtaining additional search results that match the sub-queries, including searching the additional content for the first custom search engine; generating a search result set from the initial search results and the additional search results, the generating a search result set is based on the rules for the first custom search engine and includes augmenting respective ones of the items in the initial search results with an additional search result obtained from the sub-query for the respective item in the initial search results; and providing the search result set to the requestor electronic device. 14. The method of claim 13 , wherein the obtaining the additional search results includes searching content associated with URLs that are specified in the rules for the first custom search engine.