anchor.diff:              | _ -> Set.ofSeq xs
           if set.IsEmpty then
               Regex.Empty
  -        elif RegexUtils.isCharSetHalfFull set then
  -            AllButChars <| RegexUtils.charSetFull - set
           else
               Chars set
       /// Returns a regex that recognizes any character,
  
positive.code:             | _ -> Set.ofSeq xs
          if RegexUtils.isCharSetFull set then
              Regex.Empty
          elif RegexUtils.isCharSetHalfFull set then
              Chars <| RegexUtils.charSetFull - set
          else
              AllButChars set
      /// Returns a regex specified by a string.
  
negative.code: 
  [<RequireQualifiedAccess>]
  module private RegexUtils =
      let isCharSetFull(x: char Set) = x.Count = int UInt16.MaxValue
  
      let regexEmpty = Regex.Concat []
      let regexAny = Regex.AllButChars Set.empty
  