[source]
----
"Hello world!" // <1>
----
>>>
Document
  { docMeta =
      Meta
        { docTitle = []
        , docTitleAttributes = Nothing
        , docAuthors = []
        , docRevision = Nothing
        , docAttributes = fromList [ ( "sectids" , "" ) ]
        }
  , docBlocks =
      [ Block
          mempty
          Nothing
          (Listing
             Nothing [ SourceLine "\"Hello world!\" //" [ Callout 1 ] ])
      ]
  }