anchor.diff:      let buffer = textDocument.TextBuffer
       let tagsChanged = Event<_,_> ()
       let mutable scopedSnapSpans : ScopedSpan [] = [||]
  +    let mutable oldAST = None : ParsedInput option
  +
   
       let tagTrigger () =
           tagsChanged.Trigger (self, SnapshotSpanEventArgs buffer.CurrentSnapshot.FullSpan)
  
positive.code:                                 projectionEditResolver = null,
                                  exposedSpans = exposedSpans,
                                  options = ElisionBufferOptions.None)
          
          let snapshot = hintSnapshotSpan.Snapshot
          let indentationColumn = inferIndent (hintSnapshotSpan.GetText())
          let spansToElide = ResizeArray<Span>()
          
          let startLineNumber = snapshot.GetLineNumberFromPosition(hintSnapshotSpan.Span.Start)
          let endLineNumber = snapshot.GetLineNumberFromPosition(hintSnapshotSpan.Span.End)
  
  
negative.code:         | None ->
              elisionBuffer :> ITextBuffer
  
      // drills down into the snapshot text to find the first non whitespace line
      // to display as the text inside the collapse box preceding the `...`
      let getHintText (snapshotSpan:SnapshotSpan) =
          let snapshot= snapshotSpan.Snapshot
  