anchor.diff:                  readTableCounts xs |> Option.map initTables
               | RMCons(Byte 'c'B, xs) when isTableCountsInitialized ->
                   readAndAssignIndexed readCharSet charSets xs
  -            | RMCons(Byte 'S'B, xs) when isTableCountsInitialized ->
  +            | RMCons(Byte 'S'B, xs) when isTableCountsInitialized && not hasReadAnyGroup ->
                   readAndAssignIndexed readSymbol symbols xs
               | RMCons(Byte 'g'B, xs) when isTableCountsInitialized ->
  -                readAndAssignIndexed (readGroup (itemTry symbols) (Indexed.createWithKnownLength groups)) groups xs
  +                hasReadAnyGroup <- true
  +                readAndAssignIndexed (readGroup symbols (itemTry symbols) (Indexed.createWithKnownLength groups)) groups xs
               | RMCons(Byte 'R'B, xs) when isTableCountsInitialized ->
                   readAndAssignIndexed (readProduction (itemTry symbols)) productions xs
               | RMCons(Byte 'I'B, xs) when isTableCountsInitialized ->
  
positive.code:             function
              | RMCons(String name, RMCons(UInt16 containerIndex, RMCons(UInt16 startIndex, RMCons(UInt16 endIndex, RMCons(UInt16 advanceMode, RMCons(UInt16 endingMode, RMCons(Empty, RMCons(UInt16 _nestingCount, xs)))))))) -> maybe {
                  let! containerSymbol = fSymbol containerIndex
                  let! startSymbol = fSymbol startIndex
                  let! endSymbol = fSymbol endIndex
                  let! advanceMode = match advanceMode with | 0us -> Some Token | 1us -> Some Character | _ -> None
                  let! endingMode = match endingMode with | 0us -> Some Open | 1us -> Some Closed | _ -> None
  
negative.code:             | RMCons(String _, RMCons(UInt16 7us, RMNil)) -> Unrecognized |> Some
              | _ -> None
  
          let readGroup symbols fSymbol fGroup index =
              let readNestedGroups =
                  (function | RMCons (UInt16 x, RMNil) -> fGroup x | _ -> None)
                  |> readInChunks true 1
  