The setup I envisioned is to indicate bit usage using inheritance-- the base class defines bits used by everyone.  Where you have the same bits being used by different, mutually exclusive classes, you inherit from this VALID_MESSAGE class and define additional bits you'll use.  The only difference is that you change your static access pattern from `VALID_MESSAGE.WHATEVER` to `BUBBLE_MESSAGE_TYPES.WHATEVER` and (might) reduce the chance of reusing the same bits.