Ah! I got it figured out. When Motion A is not yet complete and Motion B is invoked (shall we say “early”), then Motion A is terminated where-ever it was, and Motion B just takes over! This is a nice feature to have with the ENGINEER system. As an example, Motion A can be a “regular” motion for the robot to do, but before Motion A can be completed, some kind of emergency happens then Motion B can be launched immediately to save the robot or the operator from harm.
Another interesting note, that only an “old” user like me would know and appreciate, is that the “older” BIOLOID and MINI systems could not do this “trick”. For these older systems, once Motion A is started, and an emergency situation happens, then the only thing that the programmer could do was to set all Moving Velocities to zero to force the robot to stop “dead in its track”, next waited for Motion A to finish (time wise), then reset all Moving Velocities back to “normal”, and then finally Motion B could be played.