docs: def append_comps(comps, char):
      """
      Append a character to `comps` following this rule: a vowel is added to the
      vowel part if there is no last consonant, else to the last consonant part;
      a consonant is added to the first consonant part if there is no vowel, and
      to the last consonant part if the vowel part is not empty.
  
      >>> transform(['', '', ''])
      ['c', '', '']
      >>> transform(['c', '', ''], '+o')
      ['c', 'o', '']
      >>> transform(['c', 'o', ''], '+n')
      ['c', 'o', 'n']
      >>> transform(['c', 'o', 'n'], '+o')
      ['c', 'o', 'no']
      """
      c = list(comps)
      if is_vowel(char):
          if not c[2]: pos = 1
          else: pos = 2
      else:
          if not c[2] and not c[1]: pos = 0
          else: pos = 2
      c[pos] += char
      return c