key:
- item 1    # BLOCK-SEQUENCE-START is NOT produced here.
- item 2
# STREAM-START(utf-8)
# BLOCK-MAPPING-START
# KEY
# SCALAR("key",plain)
# VALUE
# BLOCK-ENTRY
# SCALAR("item 1",plain)
# BLOCK-ENTRY
# SCALAR("item 2",plain)
# BLOCK-END