code: func replacePlaceholders(str string, kv ...string) string {
  	for ph, value := range toMap(kv...) {
  		str = strings.Replace(str, "!!!"+ph+"!!!", value, -1)
  	}
  	return str
  }
docs: // replacePlaceholders replaces placeholders with values in kv in
  // initial str. Placeholders are in form of !!!FOO!!!, but those
  // passed here should be without exclamation marks.