It seems like we can parse $bitand and $bitor operators (distinct from the $bit operator), but they are not implemented. It kind of looks like they will trigger an exception and fail the update but not report the error to the client since last error is not set:

        default:
            stringstream ss;
            ss << "Mod::apply can't handle type: " << op;
            throw UserException( 9017, ss.str() );