Here is a list of all documented namespace variables with links to the namespaces they belong to:

BROADCAST_CAN_ADDRESS : isobus
CAN_DATA_LENGTH : isobus
CAN_PORT_MAXIMUM : isobus
DEFAULT_IDENTIFIER : isobus
DEFAULT_NAME : isobus
MAX_SEQUENCE_ID : isobus::NMEA2000Messages
NULL_CAN_ADDRESS : isobus
NULL_OBJECT_ID : isobus