docs: function transformPair(input, fn) {
    let incomingTransformController;
    const incoming = new TransformStream({
      start(controller) {
        incomingTransformController = controller;
      }
    });
  
    const pipeDonePromise = pipe(input, incoming.writable);
  
    const outgoing = transformWithCancel(async function() {
      incomingTransformController.error(new Error('Readable side was canceled.'));
      await pipeDonePromise;
      await new Promise(setTimeout);
    });
    fn(incoming.readable, outgoing.writable);
    return outgoing.readable;
  }