The OAI indexing example defines many different index names, a study of the conf/oai2index.xsl stylesheet reveals the following word type indexes (i.e. those swith suffix :w):

     any:w 
     dc_title:w
     dc_creator:w
     dc_subject:w
     dc_description:w
     dc_contributor:w
     dc_publisher:w
     dc_language:w
     dc_rights:w
    

By default, searches do access the anr:w index, but we can direct searches to any access point by constructing the correct PQF query. For example, to search in titles only, we use http://localhost:9999/?version=1.1&operation=searchRetrieve&x-pquery=@attr 1=dc_title the&startRecord=1&maximumRecords=1&recordSchema=dc

Similar we can direct searches to the other indexes defined. Or we can create boolean combinations of searches on different indexes. In this case we search for the in dc_title and for fish in dc_description using the query @and @attr 1=dc_title the @attr 1=dc_description fish. http://localhost:9999/?version=1.1&operation=searchRetrieve&x-pquery=@and @attr 1=dc_title the @attr 1=dc_description fish&startRecord=1&maximumRecords=1&recordSchema=dc