code: def add_word(self, word, freq=None, tag=None):
          
          self.check_initialized()
          word = strdecode(word)
          freq = int(freq) if freq is not None else self.suggest_freq(word, False)
          self.FREQ[word] = freq
          self.total += freq
          if tag:
              self.user_word_tag_tab[word] = tag
          for ch in xrange(len(word)):
              wfrag = word[:ch + 1]
              if wfrag not in self.FREQ:
                  self.FREQ[wfrag] = 0
          if freq == 0:
              finalseg.add_force_split(word)
docs: Add a word to dictionary.
  
          freq and tag can be omitted, freq defaults to be a calculated value
          that ensures the word can be cut out.