old_contents: # ---
  # jupyter:
  #   kernelspec:
  #     display_name: Python 3
  #     language: python
  #     name: python3
  #   language_info:
  #     codemirror_mode:
  #       name: ipython
  #       version: 3
  #     file_extension: .py
  #     mimetype: text/x-python
  #     name: python
  #     nbconvert_exporter: python
  #     pygments_lexer: ipython3
  #     version: 3.6.5
  # ---
  
  c = '''
  title: "Quick test"
  output:
    ioslides_presentation:
      widescreen: true
      smaller: true
  editor_options:
       chunk_output_type console
  '''
  
  import yaml
  print(yaml.dump(yaml.load(c)))
  
  ?next
  
new_contents: # ---
  # jupyter:
  #   kernelspec:
  #     display_name: Python 3
  #     language: python
  #     name: python3
  #   language_info:
  #     codemirror_mode:
  #       name: ipython
  #       version: 3
  #     file_extension: .py
  #     mimetype: text/x-python
  #     name: python
  #     nbconvert_exporter: python
  #     pygments_lexer: ipython3
  #     version: 3.6.5
  # ---
  
  c = '''
  title: "Quick test"
  output:
    ioslides_presentation:
      widescreen: true
      smaller: true
  editor_options:
       chunk_output_type console
  '''
  
  import yaml
  print(yaml.dump(yaml.load(c)))
  
  # ?next
  
subject: Comment out ?next