code: func (p *printer) printTrace(a ...interface{}) {
  	if !p.enableTrace {
  		return
  	}
  
  	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
  	const n = len(dots)
  	i := 2 * p.indentTrace
  	for i > n {
  		fmt.Print(dots)
  		i -= n
  	}
  	// i <= n
  	fmt.Print(dots[0:i])
  	fmt.Println(a...)
  }
docs: // ----------------------------------------------------------------------------
  // Tracing support