anchor.diff:      [<CompiledName("AdvanceByOne")>]
       let advanceByOne doUnpin (cs: CharStream) =
           if cs.CurrentIndex < uint64 cs.Source.LengthSoFar then
  -            Position.AdvanceImpl(cs.FirstCharacter, &cs.CurrentLine, &cs.CurrentColumn, &cs.CurrentIndex)
  +            cs.CurrentPosition <- cs.CurrentPosition.Advance cs.FirstCharacter
               if doUnpin then
                   cs.StartingIndex <- cs.CurrentIndex
           else
  
positive.code:     /// that starts at the first's start, and ends at the second's end.
      [<CompiledName("ConcatSpans")>]
      let concatSpans span1 span2 =
          if span1.IndexTo + 1UL = span2.IndexFrom then
              {span1 with IndexTo = span2.IndexTo}
          else
              failwithf "Trying to concatenate character span %O with %O." span1 span2
  
negative.code:     /// Creates a `CharSpan` that contains the next `idxTo` characters of a `CharStream` from its position.
      /// On the dynamic block character stream, it ensures that the characters in the span stay in memory.
      [<CompiledName("PinSpan")>]
      let pinSpan (cs: CharStream) ({CharStreamIndex.Index = idxTo}) = {
          StartingPosition = cs.CurrentPosition
          IndexTo = idxTo
      }
  
  