1. A computer-implemented method comprising: obtaining, in response to searching one or more search indexes based on a query, a ranked set of search results that includes both (i) one or more particular web search results and (ii) one or more particular custom content search results, wherein the one or more particular web search results identify respective web resources that are indexed in the one or more search indices, and wherein the one or more particular custom content search results identify respective custom content resources in a collection of resources that are exposed to a search engine by an owner of the custom content resources and that are indexed in the one or more search indexes; identifying a presentation setting for presenting combined search results that include one or more web search results and one or more custom content search results, the presentation setting specifying how to visually distinguish the one or more web search results from the one or more custom content search results on a search results page, wherein the presentation setting is specified by the owner that exposed to the search engine the collection of resources that includes the one or more custom content resources that are identified by the one or more particular custom content search results; generating, based on the presentation setting for presenting combined search results that include one or more web search results and one or more custom content search results, a search results page that includes a subset of the ranked set of search results, the subset including one or more of the particular web search results and one or more of the particular custom content search results, including visually distinguishing the one or more web search results from the one or more custom content search results on the search results page according to the presentation setting; and providing the search results page for output in response to the query.