code: public void addField(JMFType field) {
      if (field == null)
        throw new NullPointerException("Tuple field cannot be null");
      JSType newField = (JSType)field;
      if (fields == null)
        fields = new JSType[1];
      else {
        JSType[] oldFields = fields;
        fields = new JSType[oldFields.length + 1];
        System.arraycopy(oldFields, 0, fields, 0, oldFields.length);
      }
      newField.parent = this;
      newField.siblingPosition = fields.length - 1;
      fields[newField.siblingPosition] = newField;
    }
docs: Add a field to this tuple (a tuple need not have any fields).