code: func stripWhitespace(s string, margin int) string {
  	runes := []rune(s)
  	if len(s) == 0 {
  		return s // Avoid underflow below.
  	}
  	i := 0
  	for i < len(runes) && isHorizontalWhitespace(runes[i]) && i < margin {
  		i++
  	}
  	j := len(runes)
  	for j > i && isHorizontalWhitespace(runes[j-1]) {
  		j--
  	}
  	return string(runes[i:j])
  }
docs: // stripWhitespace strips whitespace from both ends of a string, but only up to
  // margin on the left hand side.  E.g., stripWhitespace("  foo ", 1) == " foo".