flags (21) are used as a "priority" for patrolling aliens inside the ship, or any alien if there is no UFO. they will search for the connected node with the highest flag value (that they didn't just come from, and no one else is headed to) and try to move towards it, for example: in battleships the commander moves between two nodes with priorities 8 and 9 repeatedly.
note that this is different from byte (23) which is sometimes also called "priority" but is used for SPAWNING and not PATROLLING
reserved (22) is used to denote what kind of behaviour should take place at the node. the only value that means anything here is 5 which means "look for base modules to destroy"