27. A system comprising: one or more computers; a computer-readable medium coupled to the one or more computers having commands stored thereon which, when executed by the one or more computers, causes the one or more computers to perform operations comprising: receiving multiple context files from one or more third-party content providers, wherein each context file contains one or more commands for controlling an operation of the search engine in processing a search query input and in presenting search results, each context file is one of a plurality of predefined context files; receiving in a search engine the search query input, the search query input received from an interface provided by one of the third party content providers; aggregating the commands in the multiple context files into a set of aggregated commands; using the aggregated commands to control an organization and a presentation of the search results resulting from the processing of the search query input, including: processing the search query input using the aggregated commands to produce a context processed search query; generating context processed search results responsive to the context processed search query; and providing the context processed search results in accordance with the aggregated commands.
27. A system comprising: one or more computers; a computer-readable medium coupled to the one or more computers having commands stored thereon which, when executed by the one or more computers, causes the one or more computers to perform operations comprising: receiving multiple context files from one or more third-party content providers, wherein each context file contains one or more commands for controlling an operation of the search engine in processing a search query input and in presenting search results, each context file is one of a plurality of predefined context files; receiving in a search engine the search query input, the search query input received from an interface provided by one of the third party content providers; aggregating the commands in the multiple context files into a set of aggregated commands; using the aggregated commands to control an organization and a presentation of the search results resulting from the processing of the search query input, including: processing the search query input using the aggregated commands to produce a context processed search query; generating context processed search results responsive to the context processed search query; and providing the context processed search results in accordance with the aggregated commands. 33. The system of claim 27 , wherein the set of aggregated commands comprises a command that specifies a document collection in which to conduct a search.