Each sub-playlist in a playlist can have unique values for a few flow controls. These include Loop and Auto-Advance. Note the two are mutually exclusive, loop implies auto-advance.
To effectively use either one, all the elements in that sub-playlist must have durations set.
This will play through the playlist, each element playing for its duration, just 1 time.
As you can probably guess, this will play through each element but then go back to the top of the sub-playlist, and do it again.