Confusion with ssh sesssion.Stdoutpipe() implemenation

Getting Help
1

As the descrption say it returns a read end of the pipe. However i was expecting it to assign the write end to sesssion.Stdout. Lets say I want to redirect stderr to same pipe for common reader consumption.
Example: sesssion.Stderr = session.Stdout. But after StdoutPipe(), sesssion.Stdout is still nil
I’m I missing something here?

// StdoutPipe returns a pipe that will be connected to the
// remote command's standard output when the command starts.
// There is a fixed amount of buffering that is shared between
// stdout and stderr streams. If the StdoutPipe reader is
// not serviced fast enough it may eventually cause the
// remote command to block.
func (s *Session) StdoutPipe() (io.Reader, error) {
	if s.Stdout != nil {
		return nil, errors.New("ssh: Stdout already set")
	}
	if s.started {
		return nil, errors.New("ssh: StdoutPipe after process started")
	}
	s.stdoutpipe = true
	return s.ch, nil
}
2

Because the usage is not what you think, its interface design is very similar to exec.
If you want to output stderr and stdout together:

func test() {
	config := &ssh.ClientConfig{} // some config
	c, _ := ssh.Dial("tcp", "127.0.0.1:22", config)
	session, _ := c.NewSession()
	// plan a
	out1, _ := session.StdoutPipe()
	err1, _ := session.StderrPipe()
	reader := io.MultiReader(out1, err1)
	// todo return reader
	// plan b
	pipeR, pipeW := io.Pipe()
	session.Stdout = pipeW
	session.Stderr = pipeW
	// todo return pipeR

	// do session.Run or other ...
}