code: public void addString(String str)
      {
          if (sourceNode != null)
          {
              addStringInternal(str);
              replaceOrRegister(sourceNode, str);
          }
          else
          {
              unSimplify();
              addString(str);
          }
      }
docs: Adds a string to the MDAG.
  
  @param str the String to be added to the MDAG