code: func (c *Config) StderrPipe() io.ReadCloser {
  	bytesPipe := ioutils.NewBytesPipe()
  	c.stderr.Add(bytesPipe)
  	return bytesPipe
  }
docs: // StderrPipe creates a new io.ReadCloser with an empty bytes pipe.
  // It adds this new err pipe to the Stderr broadcaster.
  // This will block stderr if unconsumed.