code: def add_char(self, char):
          
          if char == '\t':
              self.flush()
              self._r.add_tab()
          elif char in '\r\n':
              self.flush()
              self._r.add_br()
          else:
              self._bfr.append(char)
docs: Process the next character of input through the translation finite
          state maching (FSM). There are two possible states, buffer pending
          and not pending, but those are hidden behind the ``.flush()`` method
          which must be called at the end of text to ensure any pending
          ``<w:t>`` element is written.