anchor.diff:      match lines with
   
       // Recognize remaining types of blocks/paragraphs
  +    | SceneHeading(body, Lines.TrimBlankStart lines) ->
  +       yield SceneHeading(parseSpans body)
  +       yield! parseBlocks ctx lines
       | Section(n, body, Lines.TrimBlankStart lines) ->
          yield Section(n, parseSpans body)
          yield! parseBlocks ctx lines
  
positive.code:     | Section of int * FountainSpans
      | Span of FountainSpans
      | Lyric of FountainSpans
  
    /// A type alias for a list of blocks
    and FountainBlocks = list<FountainBlockElement>
  
negative.code:     | rest ->
          None
  
    /// Recognizes a SceneHeading (prefixed with INT/EXT, etc. or a single period)
    let (|SceneHeading|_|) = function
      //TODO: why doesn't this work? 
  //    | String.StartsWithAny [ "INT"; "EXT"; "EST"; "INT./EXT."; "INT/EXT"; "I/E"; ] heading:string :: rest ->
  //       Some(heading.Trim(), rest)
      | String.StartsWith "." heading:string :: rest ->
         Some(heading.Trim(), rest) 
      | rest ->
         None
  
  
    /// Recognizes a Lyric (prefixed with ~)
    let (|Lyric|_|) = function
      | String.StartsWith "~" lyric:string :: rest ->
  