code: func (p *printer) f(format string, args ...interface{}) {
  	if p.Err != nil {
  		return
  	}
  	if _, err := fmt.Fprintf(&p.indent, format, args...); err != nil && err != io.ErrShortWrite {
  		p.Err = err
  	}
  }
docs: // f prints a formatted message.