code: func InvalidPatternError(ctx, target string, pattern string) error {
  	msg := fmt.Sprintf("%s must match the regexp %#v but got value %#v", ctx, pattern, target)
  	return ErrInvalidRequest(msg, "attribute", ctx, "value", target, "regexp", pattern)
  }
docs: // InvalidPatternError is the error produced when the value of a parameter or payload field does
  // not match the pattern validation defined in the design.