code: private String getParentOutlineNumber(String outlineNumber)
     {
        String result;
        int index = outlineNumber.lastIndexOf('.');
        if (index == -1)
        {
           result = "";
        }
        else
        {
           result = outlineNumber.substring(0, index);
        }
        return result;
     }
docs: Return the parent outline number, or an empty string if
  we have a root task.
  
  @param outlineNumber child outline number
  @return parent outline number