[ ? complex: value ]
# STREAM_START                                  FYTT_STREAM_START
# FLOW_SEQUENCE_START                           FYTT_FLOW_SEQUENCE_START
# KEY                                           FYTT_KEY
# SCALAR value='complex key' style=PLAIN        FYTT_KEY
# VALUE                                         FYTT_SCALAR value='complex key' style=PLAIN
# SCALAR value='value' style=PLAIN              FYTT_VALUE
# FLOW_SEQUENCE_END                             FYTT_SCALAR value='value' style=PLAIN
# STREAM_END                                    FYTT_FLOW_SEQUENCE_END
#                                               FYTT_STREAM_END