anchor.diff:                  | [] -> 
                       acc, []
                   | _ ->
  -                    failwith "Invalid css selector syntax"
  +                    acc, []
  +                    //failwith "Invalid css selector syntax"
           
               let (|TokenStr|_|) (s:string) x  =
                   let chars = s.ToCharArray() |> Seq.toList
  
positive.code:                 | [] -> List.rev acc // TODO: refactor code to remove this
                  | c :: t when Char.IsLetterOrDigit c |> not ->
                      let offset = getOffset t
                      failwith (sprintf "Invalid css selector syntax (char '%c' at offset %d)" c offset)
                  | _ ->
                      failwith "Invalid css selector syntax"
              tokenize' [] source
  
      type FilterLevel = 
  
negative.code:                     selectElements' acc t
  
                  | [] -> acc
                  | _ -> []//failwith "Invalid token"
  
              selectElements' nodes tokens
  
          member public x.GetElements() =
              run()
  
  
  [<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
  module CssSelectorExtensions =
      open CssSelectors
  
      [<Extension>]
      type CssSelectorExtensions =
  