code: Vector getCounters(ElemNumber numberElem)
    {
  
      Vector counters = (Vector) this.get(numberElem);
  
      return (null == counters) ? putElemNumber(numberElem) : counters;
    }
docs: Get the list of counters that corresponds to
  the given ElemNumber object.
  
  @param numberElem the given xsl:number element.
  
  @return the list of counters that corresponds to
  the given ElemNumber object.