• compaction_level : Xapian::Compactor
• docid_order : Xapian::Enquire
• failmode : ExceptionalPostingSource , ExceptionalWeight , ExceptionalMatchSpy
• feature_flag : Xapian::QueryParser
• flags : Xapian::TermGenerator
• op : Xapian::Query
• reason : FlintLock
• sort_setting : Xapian::Enquire::Internal
• stat_flags : Xapian::Weight
• stem_strategy : Xapian::QueryParser , Xapian::TermGenerator
• test_result : test_driver