The List spec says the following about the add(String,int) method
in the Method Detail section:
    public void add(String item, int index)
      Adds the specified item to the end of the scrolling list. The
      index is zero-based. If value of the index is -1 then the item
      is added to the end. If value of the index is greater than the
      number of items in the list, the item is added at the end.
     

If the value of the index is _less than 0_ then the item is added to
the end. This should be stated in the method description for
completeness.