code: Vector putElemNumber(ElemNumber numberElem)
    {
  
      Vector counters = new Vector();
  
      this.put(numberElem, counters);
  
      return counters;
    }
docs: Put a counter into the table and create an empty
  vector as it's value.
  
  @param numberElem the given xsl:number element.
  
  @return an empty vector to be used to store counts
  for this number element.