code: public double numWithSideEffects()
    {
      int node = nextNode();
  
      return (node != DTM.NULL) ? getNumberFromNode(node) : Double.NaN;
    }
docs: Cast result object to a number, but allow side effects, such as the
  incrementing of an iterator.
  
  @return numeric value of the string conversion from the
  next node in the NodeSetDTM, or NAN if no node was found