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 with suffix :w):

     any:w
     title:w
     author:w
     subject-heading:w
     description:w
     contributor:w
     publisher:w
     language:w
     rights:w
    

By default, searches do access the any: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=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 title and for fish in description using the query @and @attr 1=title the @attr 1=description fish. http://localhost:9999/?version=1.1&operation=searchRetrieve&x-pquery=@and @attr 1=title the @attr 1=description fish&startRecord=1&maximumRecords=1&recordSchema=dc