code: function placeSlotSegs(segs) {
  	var levels = buildSlotSegLevels(segs);
  	var level0 = levels[0];
  	var i;
  
  	computeForwardSlotSegs(levels);
  
  	if (level0) {
  
  		for (i=0; i<level0.length; i++) {
  			computeSlotSegPressures(level0[i]);
  		}
  
  		for (i=0; i<level0.length; i++) {
  			computeSlotSegCoords(level0[i], 0, 0);
  		}
  	}
  
  	return flattenSlotSegLevels(levels);
  }
docs: Sets the seg.backwardCoord and seg.forwardCoord on each segment and returns a new list in the order they should be placed into the DOM (an implicit z-index).