anchor.diff:      else
         if x.HasIndex(index) then
         
  -        if x.IsDense then
  +        if isDense then
             let ii = int index
             dense.[ii].Value <- BV()
             dense.[ii].HasValue <- false
  
positive.code: 
    ///
    member private x.PutLength(newLength) =
      if x.IsDense then
        
        while newLength < length do
          length <- length - 1u
  
negative.code:   member x.NewString() = x.NewString(String.Empty)
    member x.NewString(value:string) =
      let string = SO(x)
  
      // A lot faster to set the property directly instead of going through Put
      string.Properties.[0].Value.Number <- double value.Length
      string.Properties.[0].Attributes <- DescriptorAttrs.DontEnum ||| DescriptorAttrs.ReadOnly
      string.Properties.[0].HasValue <- true
  
      string.Value.Value.Clr <- value
      string.Value.Value.Tag <- TypeTags.String
      string.Value.HasValue <- true
  