docs: def _process_repeaters(self, chars):
          '''
          Replace all repeater characters (e.g. turn サヾエ into サザエ).
          '''
          prev = None
          for n in range(len(chars)):
              char = chars[n]
              if char in rpts:
                  # The character is a repeater.
                  chars[n] = prev
  
              if char in drpts:
                  # The character is a repeater with dakuten.
                  # If the previous character can have a dakuten, add that
                  # to the stack; if not, just add whatever we had previously.
                  if prev in dkt_cvs:
                      chars[n] = dkt_lt[prev]
                  else:
                      chars[n] = prev
  
              prev = char
  
          return chars