1. A computer-implemented method comprising: receiving a search query requesting a search of custom content resources, wherein a custom content resource is a resource in a collection of resources exposed to a search engine by a user; obtaining a custom content search result that a search engine has identified in response to the search query using a custom search index generated from the collection of custom content resources exposed to the search engine by the user, the custom content search result identifying a custom content resource in the collection of resources exposed to the search engine by the user; obtaining an indication of relative importance for the custom content resource identified by the custom content search result, the indication of relative importance being a measure of importance of the custom content resource assigned by the user that exposed the collection of resources, including the custom content resource, to the search engine, the indication of relative importance indicating a measure of importance of the custom content resource relative to other resources in the collection of resources exposed to the search engine by the user; determining a score for the custom content search result based on one or more user-specified ranking parameters, the one or more user-specified ranking parameters including the indication of relative importance assigned by the user that exposed the collection of resources, including the custom content resource identified by the custom content search result, to the search engine; and ranking the custom content search result with one or more other search results using the determined score.