• compaction_level : Xapian::Compactor
• docid_order : Xapian::Enquire
• feature_flag : Xapian::QueryParser
• op : Xapian::Query
• stat_flags : Xapian::Weight
• stem_strategy : Xapian::QueryParser , Xapian::TermGenerator
• stop_strategy : Xapian::TermGenerator
• type_smoothing : Xapian::Weight