code: def triggered_token(self) -> 'CancelToken':
          
          if self._triggered.is_set():
              return self
          for token in self._chain:
              if token.triggered:
                  # Use token.triggered_token here to make the lookup recursive as self._chain may
                  # contain other chains.
                  return token.triggered_token
          return None
docs: Return the token which was triggered.
  
          The returned token may be this token or one that it was chained with.