code: def passthrough_repl(self, inputstring, **kwargs):
          
          out = []
          index = None
          for c in append_it(inputstring, None):
              try:
  
                  if index is not None:
                      if c is not None and c in nums:
                          index += c
                      elif c == unwrapper and index:
                          ref = self.get_ref("passthrough", index)
                          out.append(ref)
                          index = None
                      elif c != "\\" or index:
                          out.append("\\" + index)
                          if c is not None:
                              out.append(c)
                          index = None
                  elif c is not None:
                      if c == "\\":
                          index = ""
                      else:
                          out.append(c)
  
              except CoconutInternalException as err:
                  complain(err)
                  if index is not None:
                      out.append(index)
                      index = None
                  out.append(c)
  
          return "".join(out)
docs: Add back passthroughs.