anchor.diff:          +cell A flag indicating that the document has been syntactically parsed.
   
       +row
  +        +cell #[code is_sentenced]
  +        +cell bool
  +        +cell
  +            |  A flag indicating that sentence boundaries have been applied to
  +            |  the document.
  +
  +    +row
           +cell #[code sentiment]
           +cell float
           +cell The document's positivity/negativity score, if available.
  
positive.code: 
  +aside-code("Example").
      from spacy.tokens import Doc
      Doc.set_extension('is_city', default=False)
      assert Doc.has_extension('is_city')
  
  +table(["Name", "Type", "Description"])
      +row
  
negative.code: 
  +aside-code("Example").
      from spacy.tokens import Doc
      Doc.set_extension('has_city', default=False)
      extension = Doc.get_extension('has_city')
      assert extension == (False, None, None, None)
  
  +table(["Name", "Type", "Description"])
  