code: public Set<String> toStringSet(Set<ModificationFeature> set)
  	{
  		List<ModificationFeature> list = new ArrayList<ModificationFeature>(set);
  
  		Collections.sort(list, new Comparator<ModificationFeature>()
  		{
  			@Override
  			public int compare(ModificationFeature o1, ModificationFeature o2)
  			{
  				String t1 = getModificationTerm(o1);
  				String t2 = getModificationTerm(o2);
  
  				Integer l1 = getPositionStart(o1);
  				Integer l2 = getPositionStart(o2);
  
  				if (t1 == null && t2 == null) return l1.compareTo(l2);
  				if (t1 == null) return 1;
  				if (t2 == null) return -1;
  				if (t1.equals(t2)) return l1.compareTo(l2);
  				return t1.compareTo(t2);
  			}
  		});
  
  		return getInString(list);
  	}
docs: Sorts the modifications and gets them in a String.
  @param set modifications
  @return a String listing the modifications