anchor.diff:      let split = Utils.createHostFunction env split
       proto.Put("split", split, DontEnum)
   
  -    let substring = new Func<CommonObject, double, double, string>(substring)
  +    let substring = new Func<CommonObject, double, BV, string>(substring)
       let substring = Utils.createHostFunction env substring
       proto.Put("substring", substring, DontEnum)
   
  
positive.code:   let internal valueOf (func:FO) (this:CO) = 
      toString func this
      
    //----------------------------------------------------------------------------
    let internal charAt (this:CO) (pos:double) =
      let value = TypeConverter.ToString this
      let index = TypeConverter.ToInt32 pos
      if index < 0 || index >= value.Length then "" else value.[index] |> string
  
    //----------------------------------------------------------------------------
    let internal charCodeAt (this:CO) (pos:double) =
      let value = TypeConverter.ToString this
      let index = TypeConverter.ToInt32 pos
      if index < 0 || index >= value.Length then nan else value.[index] |> double
      
    //----------------------------------------------------------------------------
    let internal concat (this:CO) (args:Args) =
      let buffer = new Text.StringBuilder(TypeConverter.ToString this)
  
negative.code:     else
        let search = search |> TypeConverter.ToString
        value.IndexOf(search, StringComparison.Ordinal) |> double
  
    // These steps are outlined in the ECMA-262, Section 15.5.4.13
    let internal slice (this:CO) (start:double) (end':BoxedValue) =
      let S = this |> TC.ToString
      let len = S.Length
      let intStart = start |> TC.ToInteger
      let intEnd = if end'.IsUndefined then len else end' |> TC.ToInteger
      let from = if intStart < 0 then Math.Max(len + intStart, 0) else Math.Min(intStart, len)
      let to' = if intEnd < 0 then Math.Max(len + intEnd, 0) else Math.Min(intEnd, len)
      let span = Math.Max(to' - from, 0)
      S.Substring(from, span)
  
    //----------------------------------------------------------------------------
  