code: func (c *Client) cmdsx0(format string, args ...interface{}) (*sx, error) {
  	c.io.mustBeLocked()
  	if c.rw == nil || !c.connected {
  		return nil, fmt.Errorf("not connected")
  	}
  
  	cmd := fmt.Sprintf(format, args...)
  	if Debug {
  		fmt.Fprintf(os.Stderr, ">>> %s %s\n", tag, cmd)
  	}
  	if _, err := fmt.Fprintf(c.rw, "%s %s\r\n", tag, cmd); err != nil {
  		c.connected = false
  		return nil, err
  	}
  	return c.waitsx()
  }
docs: // cmdsx0 runs a single command and return the sx.  Does not redial.