a:
  123
  # impicitMappginValue

? b
  # explicitMappingKey
: c
  # explicitMappingValue

d:
  - 123
  # sequence

e:
  - 123
    # sequenceItem

f:
  - a
  # b.leadingComments
  - b
    # b.endComments
  - c
    # c.endComments
  # sequence.endComments
# documentBody.children

empty_content:
  # hello world