code: func MethodNotAllowedError(method string, allowed []string) error {
  	var plural string
  	if len(allowed) > 1 {
  		plural = " one of"
  	}
  	msg := fmt.Sprintf("Method %s must be%s %s", method, plural, strings.Join(allowed, ", "))
  	return ErrMethodNotAllowed(msg, "method", method, "allowed", strings.Join(allowed, ", "))
  }
docs: // MethodNotAllowedError is the error produced to requests that match the path of a registered
  // handler but not the HTTP method.