code: def split_phonemes(letter, onset=True, nucleus=True, coda=True):
      
      if len(letter) != 1 or not is_hangul(letter):
          raise ValueError('Not Hangul letter: %r' % letter)
      offset = ord(letter) - FIRST_HANGUL_OFFSET
      phonemes = [None] * 3
      if onset:
          phonemes[0] = ONSETS[offset // (NUM_NUCLEUSES * NUM_CODAS)]
      if nucleus:
          phonemes[1] = NUCLEUSES[(offset // NUM_CODAS) % NUM_NUCLEUSES]
      if coda:
          phonemes[2] = CODAS[offset % NUM_CODAS]
      return tuple(phonemes)
docs: Splits Korean phonemes as known as "자소" from a Hangul letter.
  
      :returns: (onset, nucleus, coda)
      :raises ValueError: `letter` is not a Hangul single letter.