Splits take a stage and divide the frame at that stage into subsets. A different sampling technique is applied to each subset. So, the highest level element after the initial sample description elements is the stage and its frame, then split and subset definitions of the frame within the stage, then sampling technique on each frame subset. Once a split occurs, then each subset can have stages underneath, and the number of stages under each split subset may differ. Move this element under SplitCondition.