/*
 *  call-seq:
 *     searcher.explain(query, doc_id) -> Explanation
 *
 *  Create an explanation object to explain the score returned for a
 *  particular document at +doc_id+ in the index for the query +query+.
 *
 *  Usually used like this;
 *
 *    puts searcher.explain(query, doc_id).to_s
 */
static VALUE
frt_sea_explain(VALUE self, VALUE rquery, VALUE rdoc_id)
{
    GET_SEA();
    Query *query;
    Explanation *expl;
    Data_Get_Struct(rquery, Query, query);
    expl = sea->explain(sea, query, FIX2INT(rdoc_id));
    return Data_Wrap_Struct(cExplanation, NULL, &expl_destroy, expl);
}