code: public static IWord create(String param)
      {
          if (param == null) return null;
          if (param.startsWith("[") && !param.startsWith("[/"))
          {
              return CompoundWord.create(param);
          }
          else
          {
              return Word.create(param);
          }
      }
docs: 根据参数字符串产生对应的词语
  @param param
  @return