anchor.diff:      /// The range is closed.
       member x.Between from upTo =
           if from > upTo then
  -            invalidArg "upTo" "'upTo' must be bigger or equal to 'from'"
  +            invalidArg (nameof upTo) "'upTo' must be bigger or equal to 'from'"
           Regex.Join(x.Repeat from, x.Optional().Repeat <| upTo - from)
       /// Returns a regex that recognizes at least a number of
       /// consecutive strings that are recognized by the given regex.
  
positive.code:             |> Seq.ofArray
              |> Seq.collect (function | Concat x -> x | x -> [x])
              |> List.ofSeq
              |> Concat
      /// Returns a regex that recognizes either a string of the first or the second given regex.
      member x1.Or x2 =
          match x1, x2 with
  
negative.code:         str
          |> Seq.map Regex.Literal
          |> List.ofSeq
          |> function | [x] -> x | x -> Concat x
      /// Returns a regex that only recognizes a single literal character.
      static member Literal c = Set.singleton c |> Chars
      /// Returns a regex that recognizes only one character
  